305 


EXCHANGE 


The  Anomalous  Osmose  of  Solutions  of 

Electrolytes  with  Collodion 

Membranes 


A  DISSERTATION 


SUBMITTED  IN  PARTIAL  FULFILLMENT  OF  THE  REQUIREMENTS 
FOR  THE  DEGREE  OF  DOCTOR  OF  PHILOSOPHY 
IN  THE  UNIVERSITY  OF  MICHIGAN 


By 

Dwight  Clark  Carpenter 
1921 


The  Anomalous  Osmose  of  Solutions  of 

Electrolytes  with  Collodion 

Membranes 


A  DISSERTATION 


SUBMITTED  IN  PARTIAL  FULFILLMENT  OF  THE  REQUIREMENTS 
FOR  THE  DEGREE  OF  DOCTOR  OF  PHILOSOPHY 
IN  THE  UNIVERSITY  OF  MICHIGAN 


By 

Dwight  Clark  Carpenter 
1921 


CONTENTS. 

I.  History 5 

II.  Purpose  of  Investigation 15 

III.  Relationship  between  Osmose  and  Electrical  Properties  of  Membrane..  16 

Preparation  of  Membrane 16 

Construction  and  Assembly  of  Cell 18 

Osmose  of  Solutions  of  Chlorides  of  Different  Metals 21 

Osmose  of  Solutions  of  Potassium  Salts  of  Inorganic  Acids 21 

Osmose  of  Solutions  of  Potassium  Salts  of  Organic  Acids 23 

Osmose  of  Solutions  of  Hydrochloric  Acid  and  of  Sodium  Hydroxide 24 

Measurement  of  Cell  Potential 24 

Sign  of  Membrane  Charge 26 

General  Discussion  and  Conclusions 27 

IV.  Relationship  between  Membrane  Pore  Size,  Osmose  and  Rate  of  Salt 
Diffusion  through  the  Membrane 29 

Permeability  of  Membranes 30 

Measurement  of  Membrane  Pore  Size 32 

Osmose  through  Membranes  of  Different  Degrees  of  Permeability 33 

Summary 37 

Diffusion  of  Solute  into  Water  Compartment  during  Osmose 41 

Summary 44 

V.  Effect  of  Stirring  Solutions  during  Osmose 46 

Apparatus 47 

Construction  and  Assembly  of  Rocking  Cell 47 

Thermostat  and  Rocking  Machine 49 

Method  of  Setting  Up  Cell  for  Experiment 49 

Osmose  Results  in  the  Rocking  Cell 51 

Passage  of  Salt  through  Membrane  during  Osmose  in  the  Rocking  Cell. .  .  52 

Summary 54 

VI.  General  Summary ! 56 


The  author  wishes  to  acknowledge  his  indebtedness  and 
gratitude  to  Professor  Floyd  E.  Bartell,  under  whose  direction 
this  research  was  carried  out,  in  sincere  appreciation  of  ex- 
cellent advice,  kindly  encouragement,  and  many  favors 
throughout  the  course  of  the  work. 


THE     ANOMALOUS     OSMOSE     OF     SOLUTIONS     OF 
ELECTROLYTES    WITH    COLLODION    MEMBRANES 


BY  DWIGHT  CLARK  CARPENTER 

I.     HISTORY 

The  phenomenon  of  osmosis,  or  the  unequal  rate  of  passage 
of  two  liquids  through  a  membrane  which  separates  them, 
was  discovered  by  the  Abbe  Nollet1  in  1748.  After  filling  a 
vessel  with  alcohol,  closing  the  orifice  with  bladder,  and  sub- 
merging in  pure  water,  he  observed  that  the  bladder  became 
distended,  thereby  showing  that  water  had  passed  through 
the  membrane  more  rapidly  than  alcohol. 

This  observation  attracted  little  attention  of  scientists 
for  over  half  a  century,  and  was  evidently  forgotten  until 
Sommering,2  experimenting  with  a  pig's  bladder,  made  a 
similar  discovery.  He  found  that  when  a  pig's  bladder, 
filled  with  an  alcohol-water  solution  was  suspended  in  air,  the 
alcohol  became  more  concentrated.  When  the  experiment 
was  repeated  substituting  a  rubber  bag  for  the  bladder,  the 
alcohol  became  more  dilute.  This  appears  to  have  been  the 
first  recorded  observation  of  anomalous  osmose.  The  above 
effects,  the  opposite  of  each  other,  established  the  important 
fact  that  the  nature  of  the  membrane  material  itself  was  an 
influencing  factor. 

The  first  quantitative  experiments  on  osmosis  were  carried 
out  by  Dutrochet3  and  Vierordt4  between  the  years  1826  and 
1848.  They  both  found  that  when  a  salt  solution  was  sep- 
arated from  water  by  a  membrane  of  pig's  bladder,  the  water 
passed  through  the  membrane  more  rapidly  than  the  salt 
solution,  resulting  in  a  hydrostatic  pressure.  As  this  pressure 

1  Xollet:  Memoires  de  1'Academy  Roy  des  Sciences,   1748,  57-104. 

2  Sommering :  Pogg.  Ann.,  28,  17  (18l'4). 

3  Dutrochet:  Ann.  Chem.  Phys.,  35,  37,  48,  49,  51,  69. 

4  Vierordt:  Pogg.   Ann.,    73,   519    (1848). 


was  the  result  of  osmosis,  it  was  termed  osmotic  pressure. 
It  was  early  recognized  that  the  experimentally  determined 
pressure  was  a  resultant  of  the  movement  of  both  the  solution 
and  the  water.  Dutrochet  gave  us  our  nomenclature  of  these 
two  oppositely  moving  liquids.  The  flow  inward  toward  the 
more  concentrated  side,  he  called  the  endosmotic  current,  and 
the  outward  flow,  the  exosmotic  current.  The  terms  osmose 
and  osmosis  are  now  used  to  denote  the  process  as  a  whole. 
In  1827  Dutrochet5  announced  an  electrical  theory  to  explain 
osmosis.  He  believed  that  the  two  sides  of  the  membrane 
developed  different  "degrees  of  electricity,"  but  that  this 
difference  could  not  be  detected  with  a  galvanometer. 

The  work  of  Dutrochet  and  Vierordt  showed  that  the  rate 
of  passage  of  pure  water  through  the  membrane  depended 
not  only  on  the  salt  used,  but  also  on  the  concentration  of  the 
salt  solution.  From  his  later  experiments  with  porous  inorganic 
membranes,  Dutrochet  concluded  that  osmosis  was  also 
dependent  on  the  nature  of  the  membrane  used. 

A  number  of  explanations  to  account  for  this  phenomenon 
were  brought  forward  by  various  investigators.  Poisson6 
believed  that  capillarity  was  the  determining  factor  in  osmosis. 
Briicke7  considered  it  due  to  relative  "attraction"  of  the  mem- 
brane for  the  two  liquids.  Jolly8  advanced  a  theory  of  hydro- 
diffusion,  in  which  he  claimed  that  the  exosmotic  current  was 
replaced  by  the  endosmotic  current  of  water,  which  was 
characteristic  of  water  and  independent  of  the  concentration . 
His  final  conclusion  was  that,  in  a  given  time,  the  amount  of 
diffused  substance  was  dependent  on  membrane  area,  the 
density  of  the  solution,  and  the  attraction  of  the  separated 
substances  for  the  membrane  and  for  each  other.  Almost 
simultaneously,  Liebig9  gave  reasons  for  believing  that  osmose 
was  due  to  the  ability  of  the  membrane  to  absorb  the  sep- 
arated liquids.  This  directed  the  trend  of  investigation  toward 

5  Dutrochet:  Ann.   Chem.   Phys.,  35,  393   (1827). 

6  Poisson:  Ibid.,   35,   98    (1827). 

7  Briicke:  Pogg.  Ann.,  58,  27  (1843). 

8  Jolly:  Ibid.,  78,  261   (1849). 

9  Liebig:  Ann.  Chem.  Phys.,  (3)  25,  367  (1849). 


the  study  of  different  membranes  and  their  function  in  the 
osmotic  process. 

Thomas  Graham10  in  1855  published  much  data  on  osmosis 
with  both  organic  and  inorganic  membranes.  He  advanced 
the  theory  that  an  alteration  of  the  membrane  was  an  indis- 
pensible  condition  to  the  maintenance  of  the  "osmotic  force." 
He  thought  one  side  of  the  membrane  was  always  acid  and  the 
opposite  side  alkaline,  and  that  the  direction  of  the  endos- 
motic  current  was  from  the  acidic  to  the  basic  side ;  or  when  the 
osmose  of  acids  and  bases  were  tested,  the  direction  of  flow 
was  alway  toward  the  side  of  lesser  acidity  in  the  former  case, 
and  toward  the  more  basic  side  in  the  latter.  In  the  develop- 
ment of  this  generalization,  Graham  did  not  include  the  results 
he  obtained  with  porous  earthenware  membranes,  for  the 
reason  that  the  osmotic  effects  observed  with  these  membranes 
were  usually  opposite  to  the  effects  obtained  with  organic 
membranes.  He  had  no  satisfactory  explanation  to  account 
for  this  difference.  Later,  influenced  by  his  own  work  on 
dialysis  and  by  that  of  I/Hermite11  on  selective  or  preferential 
solubility  of  two  liquids  in  a  separating  membrane,  Graham 
came  to  the  same  conclusions  as  those  of  Liebig. 

M.  Trabue12  prepared  a  membrane  from  a  non-setting 
glue  treated  with  tannic  acid,  which  was  the  first  artificial 
septum,  permeable  to  water  but  impermeable  to  a  crystalloid. 
He  also  prepared  a  number  of  precipitation  membranes  of 
different  permeability.  Pfeffer13  devised  the  method  of  form- 
ing precipitation  membranes  within  the  walls  of  porous  earthen- 
ware, thereby  forming  cells  which  were  capable  of  withstanding 
great  pressures.  With  these  cells  Pfeffer  performed  his  classic 
experiments  on  the  osmotic  pressure  of  sugar  solutions.  His 
work  proved  that  the  osmotic  pressure  varied  as  the  sugar 
concentration  varied.  Many  investigators  have  since  con- 
firmed Pfeffer's  measurements. 


10  Graham:  Ann.  Chem.  Phys.,   (3)  45,  17  (1855). 

11  L'Hermite:  Ibid.,  (3)  43,  420  (1855). 

12  Traube:  Archiv.  Anat.  Phys.  Und  Wissensch.  Medizin.,  1867,  87. 

13  Pfeffer:  Osmotische  Undersuchungen,  Leipzig,  1877. 


8 

Up  to  this  time  Van't  Hoff14  had  been  studying  gases 
and  chemical  equilibrium  in  solution  with  a  view  of  throwing 
light  on  the  question  of  chemical  affinity.  He  recognized 
the  close  analogy  between  gases  and  dilute  solution.  This 
analogy  between  the  behavior  of  such  widely  differing  materials, 
led  him  to  turn  his  attention  to  Pfeffer's  data  on  the  osmotic 
pressure  of  dilute  solutions  and  to  compare  osmotic  pressure 
with  gas  pressure.  From  Pfeffer's  data  he  showed  that  the 
osmotic  pressure  of  a  dilute  solution  was  equal  to  the  pressure 
which  the  dissolved  substance  would  exert  if  present  in  the 
gaseous  state  and  present  in  the  same  volume  as  that  occupied 
by  the  solution.  This  generalization  has  been  extended  to 
electrolytes  by  taking  into  account  the  increased  number  of 
solute  particles  produced  by  the  dissociation  of  the  electrolyte 
in  solution.  Van't  Hoff  was  not  concerned  with  the  mechanism 
of  osmosis,  but  simply  in  the  quantitative  relationships  existing 
between  gaseous  and  osmotic  pressures. 

The  majority  of  investigators  in  the  field  of  osmosis, 
since  the  time  of  Van't  Hoff,  have  directed  their  attention  to 
the  cause  of  osmosis  and  membrane  permeability.  L'Hermite11 
offered  the  first  explanation  of  membrane  permeability.  His 
theory  was  that  of  selective  or  preferential  solution  of  the 
two  separated  liquids  in  the  membrane.  Traube12  believed 
that  semipermeable  membranes  acted  like  atomic  sieves, 
permitting  molecules  of  a  certain  size  to  pass  through  but 
preventing  the  passage  of  larger  particles.  However  it  has 
been  demonstrated  by  Bigelow  and  Bartell,15  later  by  Bartell,16 
and  again  by  Bigelow  and  Robinson,17  and  also  by  Tinker,18 
that  osmotic  phenomena  were  obtainable  with  membranes 
the  pore  diameters  of  which  were  much  larger  than  molecular 
dimensions.  H.  B.  Armstrong19  advanced  the  theory  that  some 
kind  of  chemical  association  between  the  membrane  pores 

14  Van't  Hoff:  Zeit.  Phys.  Chem.,  1,  481  (1887). 

15  Bigelow  and  Bartell:  J.  Am.  Chem.  Soc.,  31,  1194  (1909). 

16  Bartell:  J.  Phys.  Chem.,  15,  659  (1911). 

17  Bigelow  and  Robinson,  Ibid.,  22,  99,   153  (1918). 

18  Tinker:  Proc.  Roy.  Soc.,  92A,  357  (1916). 

19  Armstrong:  Ibid.,  81B,  94  (1909). 


and  water  took  place  which  prevented  the  passage  of  any 
hydrolated  molecules  of  solute  but  had  no  effect  on  unhydro- 
lated  substancs.  The  most  generally  accepted  explanation 
has  been  that  of  L/Hermite,  whose  view  has  been  supported 
by  a  large  number  of  experiments  described  by  Nernst,20 
Kahlenberg,21  Flusin,22  and  others. 

According  to  Findley,23  theories  accounting  for  osmosis 
have  generally  fallen  into  two  classes.  One,  the  kinetic  in- 
terpretation, considers  that  osmotic  pressure  is  due  to  bom- 
bardment of  the  semipermeable  membrane  by  the  imprisoned 
solute  molecules,  analogous  to  the  kinetic  explanation  of 
gaseous  pressure.  The  other  view  is  that  the  osmotic  pressure 
is  the  hydrostatic  pressure  produced  by  the  passage  of  solvent 
into  the  solution.  This  latter  explanation  has  been  the  most 
useful  in  the  experimental  study  of  osmosis,  and  defines  the 
osmotic  pressure  as  the  hydrostatic  pressure  produced  by  the 
entrance  of  solvent  into  the  solution.  In  negative  osmose, 
the  reverse  is  the  case. 

The  mechanism  of  the  osmotic  process  has  been  explained 
in  many  ways.  In  1891  Jager24  proposed  the  surface  tension 
theory.  Although  the  theory  has  since  been  subjected  to 
numerous  modifications,  in  its  simplest  form,  it  stated  that  the 
osmotic  pressure  was  proportional  to  the  difference  in  surface 
tension  between  the  solution  and  the  pure  solvent.  Several 
years  after  this,  Callender25  proposed  the  vapor  pressure  hy- 
pothesis, according  to  which  the  membrane  capillaries  were 
regarded  as  not  wetted  by  liquids,  but  rather  that  they  acted 
as  vapor  pressure  sieves.  Perrin26  and  Girard27  considered 
that  osmosis  was  controlled  chiefly  by  electrostatic  phenomena. 

It  must  be  borne  in  mind  that  Van't  Hoff's  generalization 

20  Nernst:  Zeit.  Phys.  Chem.,  6,  35  (1890). 

21  Kahlenberg:  J.  Phys.  Chem.,  10,  141   (1906). 

22  Flusin:  Ann.  Chem.  Phys.,   (8)   13,  480  (1908). 

23  Findley:  Osmotic  Pressure,  p.  99  (1919). 

24  Jager:  Werner,  Ber.,   100,  245,  493   (1891). 

25  Callender:  Proc.  Roy.  Soc.,  (A)  80,  466  (1908);  Proc.  Roy.  Inst.,  19, 
485  (1911). 

26  Perrin:  Compt.  rend.,    136,   1388   (1903). 

"Girard:  Ibid.,    146,  927    (1908);   150,   1444   (1910);     153,  401    (1911). 


10 

was  developed  from  Pfeffer's  data  on  the  osmosis  of  dilute 
sugar  solutions,  and  was  applied  rigidly  only  to  such  dilute 
non-electrolytes,  and  only  in  the  case  of  perfectly  semiper- 
meable  membranes.  Such  membranes  are  seldom  realized  in 
actual  practice,  and  in  the  vital  processes  of  living  organisms, 
the  group  of  cells  which  seem  to  act  as  osmotic  membranes,  are 
more  or  less  permeable  to  the  solute.  The  tendency  of  elec- 
trolytes to  produce  osmotic  pressures  of  serious  non-conformity 
to  the  gas  laws  has  often  been  detected  when  refined  measure- 
ments were  made.  Lord  Berkeley  and  E.  G.  J.  Hartley28 
found  abnormal  osmotic  pressures  with  solutions  of  calcium, 
strontium  and  potassium  ferrocyanides,  and  to  explain  these 
anomalies  they  assumed  that  the  salts  existed  as  ionized 
double  molecules.  H.  N .  Morse29  found  that  membranes  which 
proved  satisfactory  for  finding  the  osmotic  pressure  of  sugar 
solution,  failed  to  give  the  quantitative  results  expected  with 
alkali  chlorides.  Moreover  after  standing  for  some  time  with 
these  chloride  solutions  in  them,  the  cells  were  greatly  impaired 
•for  use  again  with  sugar.  A  cell  returned  very  nearly  to  its 
original  condition  after  soaking  in  water  for  several  months. 
Fouard30  and  others  have  noticed  this  same  lack  of  agreement 
between  the  experimental  and  calculated  osmotic  pressures  of 
solution  of  electrolytes. 

This  anomalous  behavior  of  solutions  of  electrolytes  has 
more  often  been  noticed  by  the  biologist  and  physiologist  than 
by  the  chemist.  The  striking  behavior  of  salt  solutions  with 
cells  and  tissues  in  the  presence  of  acid  or  alkali,  has  been  a 
problem,  difficult  of  explanation  and  has  been  studied  by  Loeb,31 
Osterhout,32  Lillie,33  Girard,34  and  others.  The  swelling  of 

28  Berkeley  and  Hartley:  Phil.  Trans.,  (A)  209,  177,  319  (1908). 

29  Morse:  Osmotic  Pressures  of  Aqueous  Solutions,  Carnegie  Institution 
of  Washington,  p.  211-217  (1914). 

30  Fouard:  Bull.  Soc.  Chem.,  (4)  11,  249-261  (1912). 

31  Loeb:  Science,  37,  428  (1913). 

32  Osterhout:  Biol.  Chem.,  19,  493,  561  (1914). 

33  Lillie:  Am.  Jour.  Physiol.,  194,  (1911). 

34  Girard:  Compt.  rend.,  148,  1047,  1186  (1909);  151,  99  (1910);  153,  946 
(1911);  J.  Phys.  Path.  Gen.,  13,  359  (1911);  Compt.  rend.,  155,308  (1912);  156, 
1401  (1913);  159,  376  (1914);  167,  351  (1918);  168,  1335  (1919);  169,  92  (1919) 


11 

muscular  tissue  and  of  typical  gels  has  been  studied  by  M. 
Fischer,35  Lloyd,36  and  others.  Girard  studied  the  osmotic 
pressures  of  electrolytes  with  porous  CrCl3,  gelatin,  frog  skin 
and  other  membranes.  He  found  that  the  osmotic  pressure 
of  electrolytes  varied  greatly  with  their  nature,  as  well  as  with 
their  concentration.  He  obtained  different  results  with  differ- 
ent membranes,  and  in  some  cases  recorded  even  negative 
osmose.  Bartell37  also  observed  both  positive  and  negative 
effects  at  various  concentrations  of  acetates,  chlorides,  nitrates 
and  sulfates  when  porcelain  membranes  were  used.  In  seeking 
an  explanation  of  this  type  of  anomalous  behavior,  Girard 
enunciated  his  electrostatic  theory.  He  considered  the  osmosis 
of  electrolytes  to  be  essentially  due  to  electrical  influences 
and  the  osmotic  process  to  be  dependent  upon  the  same  general 
causes  as  electro-osmose,  namely  to  the  sign  of  the  electrically 
charged,  movable,  liquid  layer  adjacent  to  the  oppositely 
charged  walls  of  the  membrane  capillaries,  and  to  the  potential 
difference  existing  between  the  two  faces  of  the  membrane.  He 
considered  the  charge  on  the  capillary  wall  to  be  due  to  a 
small  excess  of  hydrogen  or  hydroxyl  ions,  the  movable  liquid 
layer  assuming  an  equal  but  opposite  charge.  Later  work 
convinced  him  that  the  membrane  charge  could  be  altered  by 
ions  other  than  hydrogen  and  hydroxyl.  Girard  found  that 
the  contact  potential  between  two  solutions  may  be  raised  or 
lowered,  or  that  the  orientation  of  the  potential  might  even  be 
reversed  by  the  intercalation  of  a  membrane.  Other  examples 
of  such  potential  differences  exhibited  by  membranes  are  found 
in  the  work  of  Loeb,38  Brunnings,39  Lillie40  and  Beutner41. 
Thus  the  membrane  seems  to  play  an  important  part  in  de- 
termining the  nature  of  the  osmotic  effect  and  of  the  electrical 
state  of  the  cell  system.  This  indicates  a  close  relationship  be- 

35  Fischer:  Oedema  and  Nephritis,   1915. 

36  Lloyd:  Proc.  Roy.  Soc.,  89B,  277  (1916);  Biochem.  J.,  14,  147  (1920). 

37  Bartell:  J.  Am.  Chem.  Soc.,  36,  646  (1914). 

38  Loeb:  Science,  34,  884  (1911). 

39  Brunnings:  Pfluger's  Archiv.,  48,  241  (1903);  117,  409  (1907). 

40  Lillie:  Loc.  cit. 

41  Beutner:  J.  Phys.  Chem.,  17,  344  (1913). 


12 

tween  electro-osmose  and  ordinary  osmose.  The  most  striking 
similarity  between  the  two  phenomena  is  found  in  the  reversal 
of  flow  of  liquid  and  in  the  resulting  change  of  the  cell  potential 
due  to  the  effect  of  acid,  base  and  polyvalent  ions.  The  re- 
lationship existing  between  the  hydrostatic  pressure  and  the 
H.  M.  F.  of  the  electro-osmotic  cell  system  has  been  stated  by 
Wiedemann,42  briefly  as  follows, — for  a  given  material,  the  dif- 
ference in  hydrostatic  pressure  maintained  between  the  two  sides 
of  a  porous  diaphragm  is  proportional  to  the  applied  potential. 
Wiedemann43  stated  that  Munch  obtained  reversal  of 
flow  to  the  anode  with  dilute  solutions  of  both  neutral  and 
acidified  K2CrO4.  Perrin26  from  his  work  on  electro-osmose 
came  to  the  conclusion  that  the  acidity  or  alkalinity  of  the 
solution  was  one  of  the  important  factors.  With  a  membrane 
of  porous  chromic  chloride,  acid  solutions  flowed  to  the  anode 
while  alkalies  flowed  to  the  cathode.  He  also  found  with 
cotton  wool  as  a  diaphragm  that  both  acids  and  alkalies 
flowed  to  the  cathode,  and  that  as  the  concentration  of  an  acid 
was  increased,  the  flow  decreased,  but  did  not  reverse  in  di- 
rection. Larguier  des  Bancels44  found  that  diaphragms  of 
wool,  silk  and  cotton  cloth  were  electro-negative  against 
water.  The  negative  charge  of  each  was  increased  by  alkali 
and  no  reversals  were  observed  in  acid  solutions  except  with 
silk  in  .01  M.  HC1.  Barrett  and  Harris45  found  no  reversal 
with  agar  or  parchment  membranes,  but  record  the  acid- 
alkali  reversal  with  gelatin  which  was  similar  to  silk.  Engel- 
mann46  found  similar  variations  in  electro-osmose  with  porous 
clay,  frog's  skin,  pig's  bladder,  cat's  lung  and  potato.  It  is 
manifestly  evident  that  membranes  which  are  protein  sub- 
stances, more  or  less  amphoteric  in  general  character,  appear 
to  show  the  acid-alkali  reversal  with  greater  regularity  than 
other  membrane  substances.  Perrin's  laws  of  contact  elec- 


42  Wiedemann:  Pogg.  Ann.,  87,  321  (1852);  99,  177  (1856). 

43  Wiedemann:  Elektricitat.,  2,  153  (1883). 

44  Larguier  des  Bancels:  Compt.  rend.,  138,  898  (1904). 

45  Barrett  and  Harris:  Zeit.  Elekt.,  18,  221  (1912). 

46  Engelmann:  Arch.  Neerland,  9,  332  (1874). 


13 

trification47  appear  to  have  been  confirmed  by  an  unique  ex- 
periment known  as  the  Bose-Guillaume  phenomenon.48  If 
two  wires,  one  of  which  is  coated  with  porous  material  such  as 
gelatin,  be  placed  in  a  solution  and  the  coated  wire  given  a 
sudden  twist,  a  momentary  E.  M.  F.  is  produced,  which  is 
detectable  with  a  ballistic  galvanometer.  This  phenomenon 
may  be  interpreted  as  an  enforced  osmotic  effect,  in  which  liquid 
is  momentarily  squeezed  out  of  the  pores  of  the  wire  coating, 
and  since  the  liquid  is  charged  by  contact  oppositely  to  the 
coating  itself,  a  very  brief  separation  of  charges  occurs.  This 
gives  rise  to  a  potential  difference. 

Girard  was  convinced  from  his  work  that  the  sign  of  charge 
on  the  membrane  regulated  the  amount  of  solute  diffusing 
through  into  the  solvent.  The  correctness  of  many  of  Girard 's 
conclusions  are  rendered  somewhat  doubtful  by  the  careful 
studies  of  Hamburger.49  Hamburger  first  showed  that  par- 
titioning off  two  solutions  by  a  non-protein  membrane  such  as 
collodion  had  no  effect  whatever  on  the  contact  potential  of  the 
two  solutions.  This  was  found  to  be  the  case  with  fairly  con- 
centrated solutions  of  HC1  and  Ce(NO3)3,  materials  furnish- 
ing ions  already  known  to  be  highly  effective  in  altering 
the  charges  on  the  majority  of  negative  colloids.  From  this 
work  it  seems  reasonable  to  conclude  that  extensive  selective 
ionic  adsorption,  at  least  for  collodion,  is  not  probable.  Ham- 
burger further  arrived  at  the  conclusion  that  the  magnitude  of 
charge  and  the  electrical  orientation  of  the  membrane  had  very 
little  influence  on  the  diffusion  rate  of  salts.  He  also  believed 
that  the  osmotic  flow  was  in  the  direction  demanded  by  the 
calculated  diffusion  potential  of  the  salt,  and  also  that  the 
magnitude  of  osmose  depended  largely  on  the  specific  effect  of 
the  salt  itself. 

It  has  been  observed  by  Bayliss50  and  McClendon51  and 


47  Perrin:  Compt.  rend.,    147,  55   (1908). 

48  Bose-Guillaume :  Compt.  rend.,   147,  53   (1908). 

49  Hamburger:  Zeit.  Physik.  Chem.,  92,  385  (1917). 

50  Bayliss:  Proc.  Roy.  Soc.,  84B,  245  (1911). 

51  McClendon:  Physical  Chemistry  of  Vital  Phenomena,  p.  113  (1917). 


14 

often  in  this  laboratory  that  the  potential  across  a  membrane 
boundary  increased  rapidly  to  a  maximum  value  and  receeded 
again  practically  to  zero,  especially  with  the  more  concentrated 
solutions.  With  thicker  membranes  such  as  porcelain,  the 
change  was  slower,  but  with  thin  membranes  the  effect  was  very 
rapid.  Bayliss  found  the  maxium  value  approximated  that 
calculated  from  Nernst's  formula.  The  rapid  fall  of  the 
potential  has  been  ascribed  to  swelling  of  the  membrane  and 
consequent  enlargement  of  the  pores.  That  this  view  is  in 
error,  is  evident  from  the  identical  effect  encountered  with 
porcelain,  the  pore  size  of  which,  it  must  be  admitted  is  con- 
stant. 

Very  recently  Loeb  52  working  with  collodion  membranes 
has  made  potential  measurements  of  osmotic  systems  of  so- 
called  gelatin  chloride  solutions  containing  HC1  and  finds 
experimentally  the  same  potential  value  as  calculated  from 
Nernst's  formula  on  the  basis  of  the  hydrogen  ion  concen- 
tration; again  demonstrating  the  B.  M.  F.  measured  to  be 
concentration  cell  and  contact  potential. 

Bartell  and  Hocker53  working  with  porcelain,  and  Bartell 
and  Madison54  with  gold  beaters  skin  membranes  came  to  the 
conclusion  that  osmosis  of  electrolytes  was  largely  controlled 
by  the  same  factors  as  those  which  are  active  in  electro-osmose, 
namely  a  fall  in  potential  along  a  membrane  pore  which  in- 
fluences the  direction  of  migration  of  the  electrically  charged 
water  layer  within  the  capillary.  They  considered  the 
source  of  this  potential  as  due  to  general  diffusion  of  solute, 
relative  ionic  migration  velocities  of  the  salt  used,  and  selective 
ionic  adsorption,  the  usual  resultant  being  a  combined  effect 
of  the  three  factors. 

The  usefulness  of  collodion  as  a  membrane  material  was 
recognized  in  1855  by  Kick55  who  used  it  in  his  studies  on  diffu- 
sion. The  ease  with  which  dialyzing  membranes  can  be  pre- 

62  Loeb:  J.  Gen.  Physiology,  3,  557  (1921). 

"Bartell  and  Hocker:  J.  Am.  Chem.  Soc.,  38,  1029,  1038  (1916). 
64  Bartell  and  Madison:  J.  Phys.  Chem.,  24,  444,  593  (1920). 
55  Kick:  Pogg.  Ann.,  94,  59  (1855). 


15 

pared  from'  collodion  has  resulted  in  its  use  by  many  biol- 
ogists. 

In  1907,  Bigelow  and  Gemberling56  found  that  Poiseuille's 
law  for  the  flow  of  liquids  through  capillaries  applied  to  col- 
lodion as  also  to  several  other  osmotic  membranes.  Mathews57 
made  a  number  of  qualitative  experiments  with  collodion  as 
an  osmotic  membrane,  and  concluded  that  it  was  not  a  truly 
semipermeable  membrane.  He  believed  that  the  direction  and 
magnitude  of  osmose  was  largely  a  question  of  solubility. 
More  recently  Loeb58  has  prepared  sacs  of  collodion  with  which 
he  has  studied  the  influence  of  electrolytes  on  the  electrifica- 
tion of  the  walls  of  the  sacs  and  also  has  studied  the  rate  of 
diffusion  of  water  through  them.  He  found  that  the  rate  of 
diffusion  of  water  was  influenced  not  only  by  the  concentra- 
tion, but  also  by  the  electrical  forces.  In  nearly  all  of  his  ex- 
periments the  collodion  membrane  was  impregnated  with  gela- 
tin and  in  this  respect  his  membranes  differed  from  those  used 
in  this  investigation. 


II.     PURPOSE  OF  INVESTIGATION. 

The  work  undertaken  in  this  investigation  may  be  classed 
under  three  heads. 

1.  The   determination   of   the   relationship   between   the 
osmose  of  a  number  of  electrolytes  and  the  electrical  proper- 
ties of  the  membrane  system  when  collodion  membranes  are 
used. 

2.  The  determination  of  the  relationship  between  mem- 
brane pore  size,  osmose,  and  the  rate  of  salt  diffusion  through 
the  membrane. 

3.  The  determination  of  the  effect  of  continuous  stirring 
of  the  solutions  on  the  rate  of  osmose  and  also  on  the  rate  of 
salt  diffusion. 


56  Bigelow  and  Gemberling:  J.  Am.  Chem.  Soc.,  29,  1576  (1907). 

57  Mathews:  J.  Phys.  Chem.,   14,  281   (1910). 

58  Loeb:  Loc.  cit. 


16 

III.     RELATIONSHIP  BETWEEN  OSMOSE  AND  ELECTRI- 
CAL PROPERTIES  OF  MEMBRANE 

Preparation  of  Membrane 

The  preparation  of  collodion  sacs  for  dialysis  has  been 
undertaken  by  many  investigators,  among  whom  Novy59  seems 
to  have  been  the  first  to  have  developed  a  satisfactory  and 
simple  technique  that  yields  sacs  similar  in  properties.  Loeb60 
has  used  collodion  membranes  which  were  formed  on  the 
inside  of  a  50  cc  Erlenmeyer  flask,  then  subsequently  removed 
after  drying  and  wetting  with  water.  It  was  found  by  us  that 
this  method  yielded  sacs  of  varying  permeability  and  thick- 
ness, also  that  different  portions  of  the  same  sac  varied  con- 
siderably in  these  respects. 

Preliminary  work  with  these  sac  membranes  revealed 
the  fact  that  to  prevent  the  partial  collapse  of  the  sac,  when 
the  filled  sac  with  its  manometer  tube  was  lowered  into  a 
dish  of  water,  the  experiments  must  be  started  under  an  hy- 
drostatic head,  which  in  itself  is  undesirable  for  the  experi- 
ment. Even  under  an  hydrostatic  head  of  20-40  mm,  small 
wrinkles  in  the  sac  were  not  eliminated,  and  one  to  five  min- 
utes were  necessary  before  the  sac  was  filled  sufficiently  to  reg- 
ister osmose  on  the  manometer.  Results  obtained  by  us 
showed  conclusively  that  a  sac  the  shape  of  which  was  not 
maintained  rigidly  would  stretch  badly,  and  in  the  case  of 
materials  giving  a  strong  osmose,  one  such  sac  was  found  to 
have  stretched  so  that  the  initial  sac  volume  was  increased  by 
8  cc  which  represents  approximately  15%  change  in  total 
volume  and  an  even  greater  percent  error  in  osmose  readings. 
The  first  problem  then  was  to  prepare  uniform  membranes  of 
any  required  permeability  and  thickness,  and  of  such  shape 
that  they  could  be  held  rigidly  in  place  in  the  osmotic 
cell. 

The  method  of  Bigelow  and  Gemberling56  for  casting  uni- 


69  Novy:  J.  Am.  Chem.  Soc.,  29,  1578  (1907). 

60  Loeb:  J.   Gen.   Physiology.,    1,   717  (1919);  2,  87,  173  (1919);  2,  387, 
659,  673  (1920). 


17 

form  flat  membranes  on  a  mercury  surface  was  found  to 
yield  excellent  results.  To  obtain  membranes  with  similar 
properties  it  was  found  necessary  to  control  the  whole  casting 
and  drying  process  within  a  closed  box.  This  was  done  in 
order  to  avoid  uneven  air  currents  and  also  to  keep  the  tem- 
perature constant. 

The  following  procedure  was  found  to  give  membranes 
of  any  desired  permeability  in  sheets  12  x  18  inches  and  of 
uniform  thickness.  100  cc  of  3  percent  soluble  gun  cotton, 
dissolved  in  a  mixture  of  75  percent  ether  and  25  percent  alco- 
hol, was  diluted  with  an  equal  volume  of  solvent  to  reduce 
its  viscosity.  This  solution  was  poured  evenly  over  clean 
mercury  in  a  shallow  pan  placed  within  the  casting  box  and 
allowed  to  evaporate  slowly.  At  25°  C  the  casting  time 
was  about  four  hours  for  a  membrane  of  medium  permeability. 
A  shorter  drying  period  yielded  more  permeable,  and  a  longer 
drying  period  or  higher  temperatures,  less  permeable  mem- 
branes. The  permeability  was  also  affected  by  varying  the 
proportion  of  water  in  the  alcohol-ether  diluent.  The  perfectly 
clear,  colorless  membrane  was  cut  away  from  the  sides  of  the 
casting  dish  with  a  razor  blade,  and  turned  the  other  side  up 
for  15  to  20  minutes.  The  air  was  then  changed  in  the  casting 
box  and  the  membrane  turned  over  several  times  at  short  inter- 
vals. Very  permeable  membranes  at  this  juncture  began  to  ap- 
pear opalescent,  while  the  less  permeable  did  not  alter  in  ap- 
pearance. The  membranes  were  then  immersed  in  water  to 
dissolve  out  the  remaining  ether  and  alcohol. 

Bigelow  and  Gemberling  have  shown  that  the  permeability 
of  membranes  prepared  in  a  somewhat  similar  manner,  in- 
creased gradually  for  about  a  month,  after  which  the  change 
was  slight.  With  a  view  to  shortening  the  curing  period, 
the  effect  of  soaking  the  membrane  in  varying  concentrations 
of  alcohol  and  water,  as  suggested  by  Brown61  was  tried. 
Such  curing  weakened  the  membranes  so  materially  that  this 
method  was  abandoned,  and  curing  in  distilled  water  which 


61  Brown:  Biochem.  J.,  9,  320,  591  (1915). 


18 

was  changed  daily  for  thirty  days  was  adopted  as  the  most 
satisfactory  procedure.  All  of  the  membranes  were  then  cut 
with  a  cork  borer,  so  as  to  fit  the  osmose  cell,  and  stored 
under  water  until  used.  The  marginal  inch  from  the  large 
cast  sheet,  by  which  the  latter  had  been  handled  during  the 
drying  and  curing  periods  was  discarded. 

Construction  and  Assembly  of  Osmose  Cell 

The  double-compartment  osmose  cell  of  the  type  used 
by  Bartell  and  Hocker,53  and  later  by  Bartell  and  Madison,54 
was  used  and  has  proved  satisfactory.  This  cell  possesses 
certain  desirable  points,  such  as  ease  of  detection  of  leakage, 
elimination  of  evaporation,  elimination  of  alteration  of  hy- 
drostatic pressure  due  to  temperature  fluctuation,  negligible 
capillary  corrections,  comparative  simplicity  and  general  ease 
of  operation. 

As  the  membrane  used  in  this  research  possessed  neither 

the  rigidity  of  porcelain,  which  could  be  wired  into  place,  nor 

„,.  ....  the  flexibility  of  gold-beaters 

skin,  which  could  be  waxed 
into  position,  and  further- 
more, had  to  be  kept  moist 
constantly,  a  different  type 
of  holder  was  of  necessity  de- 
vised. 

The    cell   used    in   this 

work  (Fig.  1)  was  constructed  of  two  glass  T-tubes  of  15  mm 
diameter,  each  of  which  was  fitted  into  a  rubber  stopper.  These 
were  fitted  in  turn  into  a  threaded  brass  collar  which  carried 
on  one  end  a  circular  brass  plate.  The  stopper  was  held  in  the 
collar  by  a  washer  secured  by  a  threaded  sleeve  which  could 
be  screwed  onto  the  collar.  The  half-cells  were  bolted  to- 
gether through  the  circular  brass  plates.  Paraffined  rubber 
stoppers  were  used  to  close  the  ends  of  the  cell  and  also  as 
connectors  for  the  osmometer  tubes.  The  assembled  cell  was 
made  fast  to  a  substantial  support. 

In  assembling  the  cell,  the  glass  T-tube  was  adjusted 


19 

so  that  the  surface  of  the  rubber  stopper  on  which  the  mem- 
brane was  to  be  placed,  projected  slightly  beyond  the  glass 
so  that  when  the  two  halves  of  the  cell  were  bolted  together, 
the  glass  T-tube  would  practically  touch  the  membrane. 
This  definitely  established  the  effective  membrane  area.  In 
order  to  exclude  the  possibility  of  loss  of  liquid  from  either  com- 
partment of  the  cell  by  leakage  around  the  edge  of  the  mem- 
brane, the  faces  of  the  rubber  stoppers  were  coated  with  three 
layers  of  rubber  cement,  the  first  two  layers  thoroughly  dried 
with  the  long  axis  of  the  cell  in  a  vertical  position,  and  the  third 
coat  dried  to  the  "gummy"  stage.  The  membrane  which  had 
previously  been  cut  out  with  a  cork  borer,  was  removed  by 
forceps  from  the  water  under  which  it  had  been  stored.  It 
was  then  dried  superficially  with  filter  paper,  placed  in  position 
on  the  prepared  stopper,  and  the  other  half  of  the  cell  was 
bolted  on.  The  bolts  were  taken  up  slowly  and  uniformly  so  as 
to  avoid  buckling  of  the  membrane.  The  cell  was  then  filled  with 
water  and  left  for  at  least  twenty -four  hours  before  being  used. 
The  volume  of  each  compartment  was  approximately  20  cc. 

The  osmometer  tubes  were  heavy-walled  glass  tubing  of 
2.5  mm  internal  diameter  and  were  calibrated  in  the  usual 
manner  with  mercury.  The  tubes  used  in  the  first  part  of 
this  work  agreed  in  specific  volume  to  within  about  five  per- 
cent, and  were  of  fairly  uniform  diameter  throughout.  A 
given  pair  of  tubes  was  always  used  with  the  same  cell. 

In  setting  up  a  cell  for  use,  the  water  was  first  emptied 
out  and  the  respective  compartments  rinsed  twice  with  the 
solutions  they  were  to  contain.  The  compartments  were 
then  filled,  and  the  osmometer  tubes,  previously  half  filled, 
were  adjusted  so  that  the  liquid  columns  were  equal.  The 
rubber  stoppers  were  then  immediately  waxed  into  place.  In 
this  work,  readings  of  the  hydrostatic  pressures  which  de- 
veloped were  taken  at  two  hour  intervals  over  a  twelve  hour 
period.  At  the  close  of  the  experiment  the  cell  was  emptied, 
washed  with  distilled  water,  and  then  filled  with  the  water. 
In  order  to  wash  the  membrane  capillaries  free  from  electrolyte, 
the  cell  was  put  under  an  hydrostatic  head  for  eight  to  ten 


20 

hours.  In  this  way  one  membrane  could  be  used  a  number  of 
times,  and  still  give  results  comparable  with  a  fresh  membrane. 
Results  with  the  two-compartment  cell,  when  the  tempera- 
ture was  accurately  controlled,  were  readily  duplicable  to 
within  one  or  two  percent. 

What  was  actually  obtained  in  this  work  was  data  showing 
the  rate  of  flow  of  solutions  through  the  membrane.  In  some 
cases  the  equilibrium  pressure  of  the  solution  (expressed  in  terms 
of  hydrostatic  pressure)  was  determined;  that  is,  readings  were 
recorded  when  the  rate  of  flow  of  liquid  through  the  membrane 
in  one  direction  was  just  balanced  by  the  rate  of  flow  in  the 
other  direction.  Such  readings  will  be  designated  as  maxi- 
mum osmose  values.  It  will  be  appreciated  that  the  compari- 
son of  the  rates  of  flow  of  different  solutions  is  by  no  means  an 
exact  way  of  comparing  the  absolute  osmotic  activity  of  the 
solutions.  It  does,  however,  give  us  a  fairly  accurate  indi- 
cation of  the  order  of  maximum  equilibrium  pressures  obtain- 
able with  these  solutions. 

Results  were  obtained  (1)  with  chlorides  of  metals  having 
different  valencies,  (2)  with  potassium  salts  having  inorganic 
acid  radicals  of  different  valencies,  (3)  with  potassium  salts 
having  organic  acid  radicals  of  different  valencies  and  (4)  with 
hydrochloric  acid  and  with  potassium  hydroxide. 

The  results  obtained  are  shown  in  Table  I.  In  this  table 
readings  obtained  at  the  end  of  the  two  hour,  six  hour,  and 
twelve  hour  periods  are  given.  A  medium  porous  membrane 
(pore  diameter  =  0.8  to  0.9  micron)  was  used.  The  salts 
were  usually  recrystallized  twice  from  a  good  grade  of  distilled 
water.  The  HC1  was  redistilled  as  "constant  boiling"  from 
C.  P.  acid.  The  KOH  was  a  Kahlbaum  product  and  was 
freed  from  carbonate  by  careful  precipitation  with  Ba(OH)2. 
There  was  a  slight  trace  of  barium  left  in  the  solution.  Stock 
solutions  of  the  electrolytes  were  made  up  with  conductivity 
water,  analyzed,  and  diluted  to  the  desired  concentration. 
Conductivity  water  was  used  in  one  compartment  of  the  cell 
in  all  experiments.  The  hydrostatic  pressure  was  recorded 
in  millimeters.  The  temperature  was  25°  C  =±=  0.5°  C. 


21 


4OO 


Osmose  of  Solutions  of  Chlorides  of  Different  Metals 
Chlorides  of  monovalent  metals  gave  a  repressed  effect 
at  0 . 1 M  con  centr ation .    This 
effect    persisted   throughout 
the  entire  12  hour  period. 

Solutions  of  chlorides  of 
bivalent  and  trivalent  metals 
at  low  concentrations  (0.01 
to  0.1M)  tended  to  give 
either  a  low  positive  or  neg- 
ative osmose,  while  the 
osmose  was  strongly  posi- 
tive at  higher  concentrations 


The  general  shape  of  the 
curve  representing  initial  os- 
mose rate,  (i.  e.,  osmose  in 
mm  at  the  end  of  a  two 
hour  period),  plotted  against 
the  logarithm  of  molar  con- 
centration, is  the  same  in  all 
cases  as  the  maximum  os- 
mose curve  (12  hour  period) 
plotted  in  the  same  manner. 
Fig.  2. 


CHLORIDES 
12  HOUR  OSMOSE 


MOLAR    CONCENTRATION 
Fig.  2 

These  curves  are  shown  in 
The  data  appear  in  Table  I. 


Osmose  of  Solutions  of  Potassium  Salts  of  Inorganic  Acids 

These  experiments  were  carried  out  to  ascertain  the  effect 
of  the  valence  of  the  anion  on  osmose.  It  was  found  that  an 
increase  in  valence  of  anion  (with  salts  which  do  not  hydrolyze 
greatly)  resulted  in  an  increase  of  the  initial  osmose  rate  and 
also  in  a  higher  maximum  osmose  value. 

In  concentrated  solutions,  readily  hydrolyzable  salts  of 
inorganic  acids  (i.  e.,  carbonate,  phosphate,  etc.)  when  com- 
pared with  slightly  hydrolyzable  salts  of  inorganic  acids  of 
equal  anion  valence,  were  found  to  give  an  abnormally  high 
osmose.  In  dilute  solutions,  the  readily  hydrolyzable  salts 


22 


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CC   C^    rH   rH   CO 


LC 


I    I 


T-H  <N  CO 


LC 
rH  00  O 


10 


1C 

d 


o 

.     "O 


•g  s 
4!  s 


d   .« 

s 


<N      OS 

ll 


co  o      *   -a 

rH   CO  ^7       oJ 

O    Q 


1C  O 


1C 


--r. 
COCOCCCSJ(MrHC-JCOrH 


0    S 

s  I 


I 


?^w 


23 


1000 


600 


\ 

INORGANIC 
POTASSIUM  SALTS 
&  HOUR  OSMOSE 


were  found  to  give  a  somewhat  lesser  osmose  than  the  slightly 
hydrolyzable  salts. 

When  osmose  is  plotted  against  logarithm  of  molar 
concentration,  the  shape  of 
the  initial  osmose  curves  is 
shown  to  be  somewhat  differ- 
ent from  the  maximum  os- 
mose curves.  The  initial  os- 
mose curve  approaches  a 
straight  line.  When  taken 
over  a  longer  time  interval, 
the  osmose  curve  is  found 
to  have  developed  into  the 
peculiar  N  shaped  curve  hav- 
ing a  minimum  at  0.1M,  as 
shown  in  Fig.  3. 


Osmose  of  Solutions  of 

Potassium  Salts  of 

Organic  Acids 

With  increasing  valence 
of  anion,  the  osmose  of  salts 
of  organic  acids  was  found  to 
increase  in  the  same  manner 
as  did  the  osmose  of  salts  of 
inorganic  acids.  (Fig.  4.) 


INORGANIC 
POTASSIUM  SALTS 
2 HOUR  OSMOSE/ 


.001  .01  .1  1. 

MOLAR    CONCENTRATION 


Fig.  3 


The  magnitude  of  the  osmose  of  potassium  salts  of  organic 
acids  was  greater  at  all  concentrations  than  of  the  salts  of 
inorganic  acids,  (i.  e.,  slightly  or  non-hydrolyzable  salts)  of 
corresponding  anion  valence.  (An  exception  is  to  be  noted 
in  the  case  of  K2C2O4  at  Q.001M  concentration,  which  gives 
lesser  osmose  but  of  the  same  order  of  magnitude,  than  the 
corresponding  concentration  of  K2SO4.) 

The  initial  osmose  curve  and  the  maximum  osmose  curve 
for  K^C2O4  when  plotted  against  log.  of  concentration  are  both 
of  the  same  shape  and  are  of  the  N  type. 

The  initial  osmose  curves  for  both  acetate  and  citrate 


24 


show  but  little  of  the  repression  tendency ;  with  time,  osmose 

is  repressed  and  these  curves  change  to  the  N  shaped  type.     In 

, , this  respect,   a  close  resem- 

8OO\ 1 1 7 7 

blance  is  noted  between  the 
behavior   of   the    potassium 
salts  of  organic  acids  and  the 
400  vo  xi     — - — /     /        j      salts  of  inorganic  acids. 

fc      /  I  /      A 

Osmose  of  Solutions  of  Hy- 
drochloric Acid  and  of 
Sodium  Hydroxide 

Hydrochloric  acid  gives 
a  low  positive  effect  which 
gradually  becomes  more  posi- 
tive with  increase  in  concen- 
tration. 

Potassium  hydroxide  at 
first  gives  increased  positive 
osmose  with  increasing  con- 
centration, but  in  concentra- 
tion greater  than  0.0 1M,  it 
shows  a  fairly  strong  nega- 
tive tendency.  At  somewhat 
higher  concentrations,  the  membrane  becomes  rapidly  disin- 
tegrated; were  it  not  for  this  fact  we  might,  reasoning  from 
our  experience  with  other  types  of  membranes,  expect  positive 
osmose  with  still  higher  concentrations. 


OffGANJC 

.  POTASSIUM  SALTS 
I2HOi/S?  OSMOSE 


ORGANIC 

POTASSIUM  SALTS 
ZHOU 7?  OSMOSE 


.001  .01  .1 

MOLA7?  CONCENTRATION 


Fig.  4 


Cell  Potential 

It  was  hoped  that  measurement  of  the  development  and 
subsequent  decline  in  cell  potential  might  be  accomplished 
while  osmose  was  actually  taking  place  under  the  usual  con- 
ditions. When  calomel  electrodes  are  used,  in  order  to  have 
the  hydrostatic  pressure  register  in  the  manometer  and  not 
continually  leak  out  around  the  glass  stop-cock  on  the  calomel 
electrode,  a  perfectly  fitting  valve  must  be  used.  Unfortu- 
nately, there  is  practically  no  conduction  through  such  a  valve 


25 


when  it  is  closed.  This  difficulty  terminated  temporarily  the 
thought  of  measuring  E.M.F.  and  osmose  on  the  same  ex- 
periment. 

The  potential  measurements  were  made  by  the  compen- 
sation method  as  described  in  a  previous  paper,53  using  calomel 
electrodes,  a  Leeds  and  Northrup  precision  potentiometer  and  a 
sensitive  galvanometer.  The  solution  side  of  the  membrane  is 

TABUS  II 

Cell  Potential 

Potential  Measured  in  Volts  Temperature  25°  C 


Electrolyte 

Concentration  of  Electrolytes 

0.001M 

0.01M 

0.1M 

1M  . 

KC1 

0 

0 

-0.005 

-0.003 

NaCl 

0.0 

0.008 

0.019 

0.030 

CaCl2 

0.032 

0.042 

0.060 

0.078 

MgCl2 

0.034 

0.050 

0.065 

0.085 

A1C1.3* 

0.032 

0.052 

0.076 

0.087 

KoSO4 

-0.031 

-0.028 

-0.055 

-0.072** 

K3FeC6N6 

-0.025 

-0.036 

-0.059 

-0.094** 

K4FeC6N6 

-0.037 

-0.050 

-0.069 

-0.097** 

K2CO3 

-0.017 

-0.020 

-0.030 

-0.041 

K3P04 

-0.030 

-0.048 

-0.064 

-0.095 

KC2H302 

-0.008 

-0.029 

-0.044 

-0.052 

K2C204 

-0.026 

-0.040 

-0.051 

-0.078 

K3C6H507 

-0.042 

-0.053 

-0.075 

-0.104 

HC1 

-0.035 

-0.062 

-0.109 

-0.157 

KOH 

-0.010 

0.032 

0.068 

0.081 

*  Concentrations  of  A1C13  were  0.002,  0.02,  0.2  and  1M. 
**  Solution  of  0.5M  concentration  used  in  this  case  instead  of  1M. 

understood  to  have  a  higher  potential  than  the  water  side  when 
the  sign  is  plus  and  a  lower  potential  when  the  sign  is 
minus. 

The  reversal  of  the  electrical  orientation  of  the  cell  system 
with  increase  in  concentration  of  KOH  appears  to  be  unique, 
in  these  experiments  and  is  the  same  condition  noticed  by 
Bartell  and  Hocker  when  using  porcelain  membranes  with 
NaOH.  With  collodion,  however,  this  reversal  occurs  at  a 
greater  dilution  than  with  porcelain. 


26 

The  electrical  orientation  appears  to  be  controlled  largely 
by  the  relative  migration  velocity  of  the  respective  ions  in 
the  solution,  and  is  a  function  of  the  concentration  as  is  de- 
manded by  Nernst's  formula.  So  far  as  data  on  ionic  veloci- 
ties are  available,  they  are  found  to  agree  with  the  expected 
direction  and  magnitude  of  cell  orientation,  with  the  exception 
of  KOH  in  dilute  solution,  and  with  K2CO3.  As  the  latter  is 
fairly  well  hydrolyzed,  we  may  expect  a  counter  potential 
to  be  set  up  by  the  KOH  produced,  which  would  account  for 
the  low  value  actually  found. 

Sign  of  the  Membrane  Charge 

It  is  possible  to  determine  the  sign  of  the  membrane 
charge  by  either  one  of  two  methods,  namely  by  electro- 
osmose  or  cataphoresis. 

The  use  of  gassing  electrodes  in  electro-osmose  experi- 
ments was  clearly  out  of  the  question  for  any  refined  work. 
Electrodes  such  as  those  developed  by  Barratt  and  Harris45 
(i.  e.,  Cu  in  saturated  CuSC>4  solution)  eliminate  gassing  and 
are  excellent,  but  cannot  be  used  in  certain  combinations 
such  as  ferrocyanides.  Although  a  great  deal  of  work  was 
done  with  collodion  membranes  with  a  modification  of  Barratt 
and  Harris'  apparatus,  and  also  by  Briggs'  method,62  the 
cataphoresis  method  was  found  to  be  more  satisfactory,  since 
it  was  dependable  and  at  the  same  time  more  rapid. 

A  quantity  of  dried  membrane  was  finely  pulverized, 
after  which  a  fairly  stable  water  suspension  of  it  was  made. 
This  suspension  was  examined  under  the  ultra  microscope, 
and  the  direction  of  migration  of  the  collodion  particles  under  an 
applied  potential  noted. 

The  direction  of  motion  of  finely  divided  collodion  par- 
ticles in  water  was  found  to  be  slowly  to  the  anode  which 
indicated  that  collodion  bears  a  small  negative  electrical 
charge  with  respect  to  water.  In  all  four  dilutions  of  each  of 
the  fifteen  electrolytes  tried,  the  collodion  was  likewise  neg- 

62  Briggs:   Jour.  Phys.  Chem.,  22,  256  (1918). 


27 


4- 
-f- 
| 

- 

* 
f 
t 

A     - 

f     ~? 

!  ] 

-    B    « 

ative.  It  also  appears  that  no  amount  of  acid  up  to  and  in- 
cluding 10M  HC1  will  cause  it  to  become  charged  positively, 
nor  will  any  concentration  of  salts  of  trivalent  cation,  such  as 
aluminum,  produce  this  effect.  This  appears  to  be  an  extreme 
case  of  an  "unprecipitable"  suspension.  These  results  con- 
firm those  of  Loeb  and  also  those  of  Gyemant,63  which  were 
obtained  by  the  electro-osmose  method.  In  this  respect 
collodion  is  different  from  any  other  membrane  we  have  used. 

General  Discussion  and  Conclusions 

It  will  be  seen  from  the  data  already  presented  that  the 
membrane  charge  and  the  orientation  of  the  cell  systems  for 
chlorides  of  Na,  Ca,  Mg  and 
Al  are  given  according  to  B 
of  Fig.  5. 

The  diagram  represents 
one  pore  through  the  mem- 
brane.  The  solution  side  is 

understood  to  be  above  the  membrane  and  the  water  be- 
neath. The  arrow  on  the  left,  pointing  up  toward  the  solu- 
tion, represents  the  normal  osmotic  tendency  while  the  one 
on  the  right  represents  the  imposed  electrical  effect.  Apply- 
ing this  idea  we  see  that  the  exosmotic  tendency  op- 
poses the  normal  osmotic  tendency  and  we  should  expect  a 
low  degree  of  positive  osmose  (Na,  Al)  or  even  a  negative 
osmose,  which  is  actually  realized  with  the  case  of  Ca  and  Mg. 
At  high  concentrations,  the  normal  osmotic  tendency  overcomes 
the  imposed  exosmotic  effect,  and  positive  osmose  results. 

The  condition  with  HC1  (also  with  KC1)  is  shown  in  A  of 
Fig.  5,  the  orientation  being  the  opposite  of  that  in  the  above 
case.  The  osmotic  tendencies  should  operate  in  the  same 
direction  and  a  high  positive  osmose  should  result.  While 
in  dilute  solutions  of  HC1,  positive  osmose  is  obtained  which 
is  of  greater  magnitude  than  with  Na,  Ca,  Mg,  and  Al,  these 
latter  substances  in  concentrated  solutions  give  an  osmose 


63  Gyemant:   Kolloid  Zeit.,  28,  103  (1921). 


28 

which  materially  exceeds  that  with  HC1.  It  might  be  argued, 
though  admittedly  not  at  all  conclusively,  that  except  in  the  case 
of  NaCl,  this  is  due  to  the  greater  number  of  ionic  units  fur- 
nished by  the  dissociation  of  the  more  complex  salts. 

The  peculiar  case  of  KOH  with  its  reversal  of  orientation 
with  change  of  concentration,  is  an  admirable  illustration  of 
the  applicability  of  the  electrical  theory.  In  dilute  solutions, 
the  condition  of  the  system  is  such  that  a  strong  positive  ten- 
dency should  result.  (A,  of  Fig.  5.)  The  results  are  in  accord 
with  this  prediction.  In  a  more  concentrated  solution,  how- 
ever, the  orientation  changes  and  conditions  are  as  in  B,  giv- 
ing a  weak  positive  effect;  with  still  higher  concentrations, 
a  strong  negative  effect  results. 

All  the  potassium  salts  studied  gave  orientations  of  the 
cell  system  corresponding  to  A,  Fig.  5,  which  would  lead 
us  to  infer  that  abnormally  positive  osmose  should  result.  This 
has  been  shown  to  be  true  (with  the  exception  of  K2C2O4)  so 
far  as  initial  osmose  rate  is  concerned.  The  maximum  osmose, 
however,  shows  that  some  factor,  of  which  time  is  an  important 
element,  plays  a  part  in  reducing  the  initial  high  osmose  rate 
to  a  considerably  lower  value. 

Summary  and  Conclusions 

1.  A   method    for   preparing   flat    collodion   membranes 
of  uniform  thickness  and  permeability  is  described.     Methods 
for    controlling    the  permeability  to   any  desired  value  are 
given. 

2.  A   non-leaking   osmotic   cell   of   two   T-shaped   glass 
compartments  of  equal  volume,  held  together  by  a  machined 
brass  coupling  which  also  holds  the  membrane  firmly  between 
the  two  compartments,  has  been  developed  and  used  success- 
fully. 

3.  The  osmose  values  obtained  with  thirteen  different 
salts,  an  acid  and  a  base  (chosen  to  show  the  relative  influence 
of  cation  and  anion  valence,  hydrolyzability  of  salt,  and  weak 
and  strong  acid  radical)  are  given  for  0.001,  0.01,  0.1,  and 
1M  concentrations. 


29 

4.  The   maximum  potential   of   each   of   these   osmotic 
systems  was  measured  and  recorded. 

5.  The  sign  of  the  membrane  charge  has  been  determined 
by  cataphoresis,  using  finely  ground  membrane  material  in 
suspension. 

6.  Consideration  of  the  data  obtained  shows  that  the 
initial  osmose  rate  of  practically  all  the  salts  examined  bears 
a  definite  relationship  to  the  electrical  properties  of  the  mem- 
brane system. 

7.  The   anomalous   effects   obtained   with   collodion   are 
very  similar  to  those  obtained  with  membranes  of  porcelain, 
of  gold  beater's  skin,  of  calf's  bladder,  and  of  parchment  paper. 
The  maximal  and  minimal  values  obtained  with  these  different 
membranes  do  not  come  at  exactly  the  same  concentrations, 
but  when  consideration  is  given  to  the  exact  condition  of  the 
electrical  orientations  of  the  different  membrane  systems,  the 
results  are  closely  comparable. 

8.  It  has  been  shown  that  anomalous  effects  are  related 
somewhat  to  the  time  factor.     For  example  the  data  for  the 
osmose  of  potassium  carbonate  at  the  end  of  a  two  hour  period, 
when  plotted  against  log  of  concentration  of  potassium  car- 
bonate gave  no  N  shaped  curve  while  the  N  shape  was  pro- 
nounced for  the  curve  obtained  at  the  end  of  a  12  hour  osmose 
period.     This  fact  makes  it  appear  probable  that  the  process 
of  diffusion  is  in  some  way  responsible  for  the  repressing  ef- 
fects noted  at  the  intermediate  concentrations. 


IV.     RELATIONSHIP  BETWEEN  MEMBRANE  PORE  SIZE, 

OSMOSE  AND  RATE  OF  SALT  DIFFUSION 

THROUGH  THE  MEMBRANE 

In  the  foregoing  section  of  the  thesis,  it  was  shown  that 
the  direction  and  magnitude  of  initial  osmose  of  solutions  of 
a  large  number  of  salts,  also  of  acid  and  alkali,  with  collodion 
membranes  were  in  accord  with  the  anomalous  osmose  theory 


'30 

as  previously  outlined  by  Bartell  and  co-workers.53'54'64  In  the 
section  above  referred  to,  attention  was  called  to  the  change  in 
shape  of  the  osmose  rate  curve  with  time.  A  so-called  straight 
line  curve  was  obtained  when  the  initial  osmose  values  (two 
hour  osmose  readings)  were  plotted  against  the  concentration, 
while  a  peculiar  N  shaped  curve  was  obtained  when  the  maxi- 
mum osmose  values  (i.  e.,  obtained  after  12  hours  or  more) 
were  plotted  against  concentration.  The  latter  exhibited  a 
minimum  point  at  about  0.1  M  concentration. 

From  the  fact  that  the  straight  line  initial  osmose  rate- 
concentration  curve  developed  into  the  N  shaped  curve 
with  time  as  the  only  apparent  influencing  factor,  it  was  in- 
ferred that  diffusion  of  electrolyte  was  the  active  factor  di- 
rectly responsible  for  the  decided  alteration  of  osmose  rate 
through  this  concentration  range. 

In  order  to  test  this  idea,  collodion  membranes  of  different 
degrees  of  permeability  were  prepared  in  the  manner  described 
in  the  previous  paper.  The  number  of  capillary  holes  through 
a  given  area  of  membrane  will  be  shown  to  be  nearly  the  same 
in  all  cases.  The  actual  diameter  of  the  capillaries  was  regu- 
lated at  the  time  of  setting  and  by  the  amount  of' evaporation 
of  solvent  which  occurred  before  soaking  in  water. 

Permeability  of  the  Membranes 

The  permeability  of  the  membranes  used  in  this  work 
was  determined  by  the  hydrostatic  method  of  Bigelow  and 
Gemberling.56  A  known  and  constant  hydrostatic  pressure 
was  applied  to  water  in  contact  with  the  membrane  and  the 
rate  of  passage  of  water  through  the  membrane  accurately 
noted  on  a  calibrated  capillary  tube  by  means  of  a  cathetometer. 
The  cells  were  sealed  with  wax  around  the  rubber  stoppers, 
so  that  leakage  was  eliminated.  They  were  then  immersed 
in  a  thermostat.  An  idea  of  the  reproducibility  of  the  col- 
lodion membranes  and  the  constancy  of  the  effective  membrane 
areas  of  the  various  cells  may  be  gathered  from  the  close  agree- 

64  Bartell  and  Sims:  J.  Am.  Chem.  Soc.,  44,  289  (1922). 


31 


TABLE  III 
Membrane  Permeability  (Very  Permeable  Membrane) 


Membrane 
no. 

Pressure 
applied, 
mm  HaO 

Water 
passed, 
cu.  mm 

Time,  sec. 

Cu.  mm  X  10  ~4  water 
passing  per  sec.  per  sq. 
cm  diaph.  area 

1 
2 
3 

4 

385 
385 
385 
385 

18.48 
19.50 
23.16 
18.90 

337 
355 
421 
344 

319 
319.3 
320 
319.5 

Average 


319.45 


Diaphragm  Area  =  171.2  sq.  mm.     Temperature  =  20°  C 


TABLE  IV 

Relative  Membrane  Permeability 
Temperature  =  20°  C 


Least  permeable  membrane 


Pressure  applied, 
mm  H2O 

Cu.  mm  X  10  ~4 
water  passing  per 
sec.  per  sq.  cm. 
dia.  area 

Cu.  mm    X  10  ~4 
water  passing  per 
sec.  per  sq.  cm.  area 
per  mm  pressure 

Relative 
permeability 

485 
385 
285 

185 

54.76 
42.93 
31.84 
21.37 

0.1129 
0.1115 
0.1117 
0.1155 

- 

Ave. 

0.1129 

1 

Medium  permeable  membrane 


492 

109.32 

0.2221 

392 

87.82 

0.2240 

292 

64.84 

0.2220 

192 

43.29 

0.2255 

0.2234 

1.978 

Very  permeable  membrane 


485 

403.10 

0.8311 

385 

319.45 

0.8297 

285 

236.20 

0.8288 

190 

158.08 

0.8320 

0.8304 

7.355 

32 

ment  of  the  results.  Absolute  results  involving  correction 
for  viscosity  of  water  at  20  °  C  were  not  attempted,  as  compara- 
tive data  at  the  one  temperature  were  all  that  was  desired  to 
establish  relative  permeability. 

The  preceding  table  was  compiled  from  average  values 
obtained  in  the  same  manner  as  shown  in  the  foregoing 
table. 

From  Poiseuille's  Law  for  the  flow  of  liquids  through  capil- 

KwPD4T 
lary  tubes,  we  have  the  expression  Q  = .     Q  represents 

L 

the  quantity  of  liquid  passing  through  n,  number  of  capillaries  of 
diameter  D  and  length  L,  in  the  time  T,  and  under  pressure  P. 
K  is  a  constant,  the  value  of  which  is  dependent  upon  the  liquid 
used,  the  temperature,  etc.  It  is  assumed  that  the  length  of 
the  capillary  pore  in  the  various  membranes  is  a  function  of  the 
thickness  of  the  membrane.  Under  the  conditions  of  the  ex- 
periment, K,  P,  and  T  may  be  combined  into  a  single  constant 

kriD* 
k  and  the  equation  rewritten  Q  =  -^ — .     If  we  assume  for 

JL/ 

the  time  being  that  n  is  a  constant  for  all  three  membranes, 
we  are  able  to  compare  the  relative  pore  diameters  of  the 
membranes. 

The  actual  thicknesses  of  the  three  membranes  were,  re- 
spectively, 0.08  mm,  0.15  mm,  and  0.31  mm. 

The  relative  diameters  of  the  pores  of  the  three  mem- 
branes, calculated  as  above,  give  the  values  1 :  1.38:  2.31. 

Measurement  of  Membrane  Pore  Size 

The  membrane  pore  size  was  measured  directly  by  the 
method,  based  on  Jurin's  Law,  as  used  by  Bigelow  and  Bartell.15 
This  gives  us  information  relative  to  the  assumption  made  con- 
cerning the  number  of  pores  in  each  of  the  membranes  used. 
In  case  the  relative  pore  diameters  as  measured  by  the  two 
independent  methods  agree,  we  are  justified  in  the  previous 
assumption  that  the  number  of  pores  in  a  given  area  of  mem- 
brane is  the  same  for  all  three  membranes. 

The  membrane  was  supported  in  a  holder  by  a  fine-mesh 


33 


wire  screen.  Owing  to  the  nature  of  the  membrane,  which 
was  somewhat  elastic,  and  which  stretched  under  the  pressure 
necessary  to  force  water  out  of  the  pores,  the  values  here 
reported  must  be  considered  as  representing  pores  which  have 
been  slightly  stretched.  Results  obtained  follow: 

TABLE  V 
Membrane  Pore  Size 


K.  Cms 
pressure  per 
sq.  cm. 

Pore 
diameter, 
microns 

Relative  Pore  Diameter 

Jurin's 
Law 

Poiseuille's 
Law 

Least  permeable 
membrane 
Medium  permeable 
membrane 
Very  permeable 
membrane 

4.23 
3.17 
1.76 

0.701 
0.934 
1.681 

1.00 

1.33 
2.39 

1.00 

1.38 
2.31 

The  above  agreement  between  the  values  for  relative  pore 
diameter,  as  determined  by  the  two  different  methods,  indi- 
cates the  validity  of  the  assumption  that  the  number  of  pores 
in  a  given  cross-sectional  area  of  the  various  membranes  is 
very  nearly  the  same,  at  least  within  3  to  4%.  We  shall 
throughout  this  paper,  distinguish  between  these  three  mem- 
branes by  referring  to  them  as  (a)  least  permeable,  (b)  medium 
permeable,  and  (c)  very  permeable. 


Osmose  through  Membranes  of  Different  Degrees  of 
Permeability 

The  validity  of  the  hypothesis  that  diffusion  was  respon- 
sible for  the  change  in  shape  of  the  osmose  rate-concentration 
curve,  may  be  tested  by  comparing  the  osmose  through  the 
membranes  of  different  permeabilities.  The  membrane  of 
least  permeability  should  show  an  initial  rate-concentration 
curve  which  approaches  more  nearly  a  straight  line  than  do 
the  curves  obtained  with  the  other  membranes  of  greater 
permeability.  The  membrane  of  medium  permeability  should 
show  less  of  the  straight  line  effect,  and  should  rapidly  develop 


34 


the  N  type  of  curve,  while  the  very  permeable  membrane 
should  probably  show  no  straight  line  effect  at  all,  but 
should  give  instead  the  N  shaped  curve  from  the  beginning. 

In'  all  of  the  work  de- 
scribed in  this  paper,  very 
carefully  selected  osmometer 
tubes  of  2.5  mm  internal 
bore  were  used.  These  were 
selected  from  among  over 
four  hundred  tubes  and  the 
volumes  of  given  lengths  of 
them  varied  not  more  than 
one  percent.  This  uniform- 
ity was  considered  satisfac- 
tory. The  duplicability  of 
osmose  experiments  with 
these  refinements  and  with 
good  temperature  control 
was  close  to  one  percent. 

Inasmuch  as  it  was  de- 
sired to  obtain  results  when 
membranes  of  different  per- 
meabilities were  used,  both 


Fig.  6 


Development  of  N  shaped  Osmose  Curve   with     representative     potas- 
as  influenced  by  time  in  case  of  KC1.          .  .  ,          .  *:«•<• 

Least  permeable  membrane.  smm  salts  wlth  amons  of  dlf- 

Time  in  hours  ferent  valencies   and  with 

salts  of  bivalent  and  triva- 

lent  metals,  the  following  were  used:  KC1,  CaCl2,  A1C13,  K2SO4, 
and  KaFeCeNe.  In  addition,  sucrose  was  also  used  in  order  to 
ascertain  how  the  osmose  of  a  substance  supposed  to  give  a 
normal  osmose  rate  was  affected  by  permeability.  One  concen- 
tration in  addition  to  those  used  in  the  previous  work  was  in- 
troduced, namely,  0.004  M.  The  recession  in  the  N  shaped 
curve  started  to  develop  with  potassium  salts  at  about  0.004  M 
concentration.  In  place  of  1  M  concentration  0.5  M  was  sub- 
stituted, the  osmose  in  this  region  of  concentration  was  of  the 
positive  type,  and  proved  to  be  of  no  special  import  in  this  in- 


35 


vestigation.  The  hydrostatic  pressure  was  read  at  thirty  min- 
ute intervals  for  the  first  two  hours,  after  which  two  hour  read- 
ings were  generally  made.  Close  watch,  however,  was  kept  on 
the  experiments  as  they  neared  the  maximum,  so  that  the  ex- 
treme pressure  developed  would  be  known.  The  accompany- 
ing Table  VI  for  KC1  contains  data  such  as  was  obtained 
for  all  solutions  investigated.  In  order  to  economize  space, 
only  values  read  at  the  end  of  2  hr.,  12  hr.,  and  at  maximum 


100 


.01  .1 

MOLAR  CONCENTRATION 

Fig.  7 

Development  of  N  shaped  Osmose  Curve 

as  influenced  by  time  in  case  of  K2SO4. 

Least  permeable  membrane. 

Time  in  hours 


.001  .01  .1 

MOLAR  COA/C£A/T/?AT/0A/ 

Fig.  8 

Development  of  N  shaped  Osmose  Curve 

as  influenced  by  time  in  case  of  K3Fe(CN)i. 

Least  permeable  membrane. 

Time  in  hours 


osmose  will  be  given.  The  development  of  the  N  shaped 
curve  with  time  is  shown  for  potassium  salts  in  Figures  6,  7, 
and  8,  the  time  being  expressed  in  hours.  The  effect  of  in- 
creasing the  membrane  pore  diameter  on  the  initial  osmose 
rate-concentration  curve  is  shown  in  Figures  9,  10,  and  11. 


36 


500 


MOLAR  CONCENTRATION 
Fig.  9 


200 


Fig.  10 


Initial  Osmose  Rate  (2  Hrs)  of  Potassium   Initial  Osmose  Rate  (2  Hrs)  of  Potassium 

Salts.  Salts. 

With  least  permeable  membrane  With  medium  permeable  membrane 


.001  .01 

MOLAR  CONCENTRATION 

Fig.  11 

Initial  Osmose  Rate  (2  Hrs)  of  Potassium     Initial  Osmose  Rate  (2  Hrs)  of  K3Fe(CN)6 

Salts.  With  membranes  of  different 

With  very  permeable  membrane  permeabilities 


37 


Figure  12  shows  the  initial  (2  hr.)  osmose  rate-concentration 
curve  for  KsFeCeNe  with  all  three  membranes. 

TABLE  VI 
Osmose  of  KC1  (Least  Permeable  Membrane) 


Osmose 
period,   hrs. 

0.001  M 

0.004M 

0.01  M 

0.1  M 

0.5M 

0.5 

2 

4 

4 

7 

18 

1 

4 

8.5 

10 

12 

32 

1.5 

6 

12 

15 

16.5 

44.5 

2 

8 

16 

19 

21 

56 

4 

13 

30 

33 

34 

74 

6 

17.5 

42 

42.2 

40 

86 

8 

21.5 

50 

49.5 

44 

93 

10 

25 

55 

54.5 

46.5 

98 

12 

28.5 

59 

57 

48 

98 

14 

28.5 

62 

— 

49.5 

— 

16 

— 

— 

59 

— 

— 

18 

— 

67 

— 

— 

— 

20 

— 

— 

59 

— 

— 

22 

— 

67 

— 

— 

— 

Summary 

The  following  generalizations  may  be  drawn  from  the  fore- 
going data: 

1.  The  least  permeable  membranes,  i.  e.,  the  ones  with  pore 
diameters  less  than  0.7  microns,  during  the  first  five  hours 
showed  a  tendency  to  give  only  positive  osmose  with  all  the 
salts  used  with  the  exception  of  CaCl2,  which  gave  a  negative 
osmose.  At  no  time  during  the  first  few  hours  did  the  N 
shaped  curve  become  pronounced.  (K2SO4  solutions  gave  a 
slight  N  shape  with  this  membrane.)  These  facts  indicate 
that  the  phenomenon  of  negative  osmose  is  not  entirely  de- 
pendent upon  the  specific  salt  used,  neither  is  it  dependent 
entirely  upon  concentration,  but  its  appearance  is  dependent 
also,  and  to  a  large  degree,  upon  the  diameter  of  the  membrane 
pores.  It  seems  probable  that  negative  osmose  does  not  oc- 
cur until  the  diameter  of  the  membrane  pore  reaches  a  certain 
limiting  value,  which  is  definite  for  a  given  salt  solution. 
In  this  work  we  have  noted  that  when  negative  tendencies  pre- 


38 


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40 

vail,  the  negative  effects  became  greater  as  the  pore  diameters 
are  increased. 

2.  With  medium  permeable  membranes    (pore   diameters 
less  than  0.9  microns),  the  N  shaped  curve  was  fairly  pro- 
nounced, though  not  obtained  throughout  the  entire  period  of 
osmose,  with  the  potassium  salt  solutions,  KC1,  K2SO4  and 
K3FeCeN6.     The  repression  in  the    curve    occurred    between 
0.004  M  and  0.1  M  concentration. 

3.  With  very  porous  membranes  (pore  diameters  less  than 
1.6  microns),  the  N  shaped  curve  became  pronounced  and  was 
maintained  throughout  the  entire  period  of  osmose,  from  the 
initial  to  the  final  reading. 

4.  It  should  be  pointed  out  that  the  N  shaped  curve  was 
obtained  even  with  the  slightly  permeable  membranes,  pro- 
vided the  experiment  was  allowed  to  continue  for  a  sufficient 
length  of  time  before  osmose  readings  were  taken.     When 
readings  were  made  at  the  end  of  a  twelve  hour  period,  a  re- 
pressing effect  was  noted  with  all  three  potassium  salts,  this 
repression  occurred  between  the  concentrations  of  0.004  M 
and  0.1  M. 

5.  With  the  least  permeable  membranes,  the  initial  os- 
mose rate  of  the  concentrated  solutions  was  greater  than  that 
obtained  when  the  very  permeable  membranes  were  used. 
On  the  other  hand,  the  rather  surprising  observation  was  made 
that  the  initial  osmose  rate  of  dilute  solutions  was  less  with  the 
least  permeable  membranes  than  with  the  very  permeable 
membranes. 

6.  The  time  required  to  reach  maximum  osmose  was  less 
with  the  very  permeable  membranes  than  with  the  less  permea- 
ble membranes.     Also,  the  maximum  osmose  attained  with 
potassium  salts  was  progressively  less  with  increasing  mem- 
brane porosity  (an  exception  in  the  case  of  KC1  with  medium 
permeable  membranes  is  to  be  noted). 

7.  The  range  of  concentration  over  which  repression  of 
osmose  occurred  was  greater  with  very  permeable  membranes 
than  with  the  less  permeable  membranes. 

8.  The  osmose  of  a  substance  of  supposedly  normal  os- 


41 

mo  tic  tendencies,  such  as  sucrose,  showed  a  decreasing  max- 
imum value  as  the  porosity  of  the  membrane  was  increased. 
No  N  shaped  curve  was  obtained  with  sucrose  solutions. 

Diffusion  of  Solute  into  Water  Compartment  during 

Osmose 

It  has  been  known  since  dialyzers  of  collodion  were  first 
used  by  Kick55  that  they  were  permeable  to  crystalloids.  For 
this  reason,  the  exosmotic  current  during  an  osmose  experi- 
ment must  be  of  considerable  magnitude.  A  study  of  the 
exosmotic  current  has  received  but  little  attention  from  re- 
cent investigators  in  osmosis. 

The  passage  of  solute  into  the  water  compartment  may 
be  regarded  as  taking  place  in  some  one  or  more  of  the  follow- 
ing ways : 

1.  Filtration,  the  passage  of  solute  through  the  membrane 
pores  due  to  hydrostatic  pressure. 

2.  Diffusion,  the  passage  of  solute  particles  through  the 
membrane  pores  due  to  their  own  motion  and  according  to 
Fick's  Law,  dependent  largely  on  the  salt,  the  concentration 
gradient  and  the  temperature. 

3.  Dissolving  of  solute  in  the  membrane  material  itself, 
the  membrane  then  giving  up  solute  to  the  water  compart- 
ment according  to  the  partition  law. 

4.  Adsorption  of  solute  from  the  contents  of  the  solution 
compartment  by  the  walls  of  the  membrane  capillary  and  then 
the  subsequent  giving  off  of  solute  by  the  membrane  to  the 
contents  of  the  water  compartment,  in  order  that  the  adsorp- 
tion process   between   membrane   and   water   may   come   to 
equilibrium  according  to  the  partition  law. 

In  the  case  of  collodion,  all  of  the  factors  may  be  active 
simultaneously,  hence  the  question  arose  which  of  these  factors 
are  the  predominating  ones.  That  this  was  a  very  intricate 
problem  can  be  seen  from  the  fact  that  diffusion,  solution, 
and  adsorption  are  quite  interdependent,  also  diffusion  and 
filtration  effects  are  not  easily  distinguishable  from  each  other. 


42 


Effect  of  a  Given  Salt  and  of  the  Pore  Diameter  of  Membrane 
on  Exosmotie  Current  or  Salt  Diffusion 

The  collodion  membranes  of  different  degrees  of  porosity 
which  had  already  been  used  in  the  foregoing  osmotic  studies 
were  used  in  this  work.  In  these  stationary  cells,  the  osmotic 
experiment  was  stopped  at  the  end  of  two  hours  and  the  con- 
tents of  the  water  compartment  removed  and  analyzed. 
Then  another  identical  experiment  was  started  and  allowed  to 


TABLE  IX 

Millimols   of   Salt  which   passed  through  Membranes  of  Different 
Permeability  during  Two  Hour  Osmose  Period 

Stationary  Cells 


Millimols  of  salt  which  passed  through 

Salt 

Initial  molar 
cone,  in  salt 
compartment 

Very  permeable 
(pore  diam.  about 
1.6  micron) 

Med.  permeable 
(pore  diam.  about 
0.93  micron) 

Least  perme- 
able (pore 
diam.  about 
0  .  7  micron) 

K3F€C6N6 

0.004 

0.0045 

0.0020 

0.00155 

0.01 

0.0129 

0.0096 

0.0090 

0.1 

0.175 

0.169 

0.164 

K2S04 

0.004 

0.00193 

0.00345 

0.0034 

0.01 

0.01205 

0.0109 

0.0144 

0.1 

0.1584 

0.155 

0.1803 

KC1 

0.004 

0.0032 

0.0018 

0.0020 

0.01 

0.0115 

0.0112 

0.0107 

0.1 

0.219 

0.190 

0.207 

CaCl2 

0.004 

0.00396 

0.00264 

0.00275 

0.01 

0.01385 

0.00835 

0.01225 

0.1 

0.173 

0.097 

0.199 

A1C13 

0.008 

0.0137 

0.0098 

0.00587 

0.02 

0.0234 

0.02736 

0.0234 

0.2 

0.311 

0.311 

0.282 

run  to  its  maximum  value,  and  the  contents  of  the  water  com- 
partment analyzed  as  before,  so  that  not  only  the  initial 
rate  (2  hour  period)  would  be  known,  but  also  the  total  amount 
of  electrolyte  which  diffused  from  the  cell  by  exosmose  during 
the  maximum  osmose  period. 

Analyses  of  KC1,   CaCl2  and  K3FeC6N6  solutions    were 


43 


done  volumetrically,  the  chlorides  by  Mohr's  method65  and 
the  ferricyanide  by  Muller  and  Diefenthaler's  method.66 
Aids  and  K2SO4  solutions  were  analyzed  gravimetrically  by 
evaporations  and  ignition;  also  by  precipitation  and  ignition 
of  A1(OH)3  and  BaSO4,  respectively. 

TABLE  X 

Millimols   of  Salt  which   passed  through  Membranes  of  Different 
Permeability  during  Maximum  Osmose  Period 

Stationary  Cells 


Salt 

Millimols  of  salts  which  passed  through 

Initial  molar 
cone,  in  salt 
compartment 

Very 
permeable 

Medium 
permeable 

Least 
permeable 

KsFeCeNe 

0.001 

0.0028 

0.0037 

0.0048 

0.004 

0.0138 

0:0163 

0.0188 

0.01 

0.0344 

0.0431 

0.0551 

0.1 

0.434 

0.529 

0.665 

0.5 

2.216 

3.042 

3.444 

KgSCU 

0.001 

0.005 

0.0025 

0.0038 

0.004 

0.016 

0.022 

0.0237 

0.01 

0.036 

0.055 

0.073 

0.1 

0.460 

0.626 

0.808 

0.5 

2.450 

3.467 

1.964 

KC1 

0.001 

trace 

trace 

0.0021 

0.004 

0.0175 

0.0235 

0.0329 

0.01 

0.0479 

0.0641 

0.0790 

i 

0.1 

0.610 

0.688 

0.836 

0.5 

3.112 

3.77 

4.265 

CaCl2 

0.001 

0.0014 

0.0010 

0.0014 

0.004 

0.0764 

0.0241 

0.0261 

0.01 

0.0476 

0.0647 

0.0837 

0.1 

0.520 

0.565 

0.682 

0.5 

2.651 

3.596 

4.30 

A1C13 

0.002 

0.0070 

0.0070 

0.0080 

0.008 

0.0293 

0.0311 

0.0332 

0.02 

0.0315 

0.104 

0.275 

09 

i  nin 

1    PV89 

.  *j 

1.0 

5.5 

1  .  U1U 

6.38 

J.  .  *jQ£i 

4.01 

Direct  comparison  of  the  total  amounts  of  salt  which 
passed  through  the  various  membranes  during  the  maximum 


65  Mohr:  Zeit.  anorg.  Chem.,  63,  330  (1909). 

66  Muller  and  Diefenthaler:   Ibid.,  67,  418  (1910). 


44 

osmose  period  was  a  difficult  matter,  inasmuch  as  the  time 
period  of  reaching  maximum  osmose  depended  not  only  on  the 
specific  salt  and  its  concentration,  but  also,  and  more  particu- 
larly, on  the  membrane  porosity.  For  this  reason,  the  amount 
of  salt  which  passed  through  the  membrane  in  a  given  time, 
say  in  two  hours,  must  be  considered  a  fairer  means  of  compar- 
ing actual  diffusion  rates.  Even  then,  comparisons  of  the  dif- 
fused salts  will  be  subject  to  some  error,  especially  when  made 
between  the  less  porous  and  the  very  porous  membranes,  since 
in  a  two  hour  period,  the  osmose  will  have  progressed  rela- 
tively further  with  the  more  porous  membranes  than  with 
the  less  porous  membranes.  Since  the  time  interval  for 
maximum  osmose  is  nearly  the  same  with  the  two  least  per- 
meable membranes,  no  appreciable  error  of  the  type  above 
indicated  will  be  probable  when  comparisons  are  made  be- 
tween them.  Such  comparisons  will  be  more  justifiable  than 
when  comparisons  are  made  between  the  least  permeable  and 
the  very  permeable  membranes. 

Summary 

The  foregoing  data  brought  out  the  following  conclusions : 

1.  The  rate  at  which  K3FeC6N6  and  A1C13  passed  through 
the  membrane  was  increased  at  all  concentrations  as  the  pore 
diameter  was  increased.     On  the  other  hand,  relative  diffusion 
values  of  K2SO4  and  CaCl2  decreased  materially  as  the  pore 
diameter  was  increased.     The  diffusing  rate  of  KC1  remained 
about  the  same  with  the  different  membranes. 

2.  In  dilute  solutions  K2SO4,  CaCl2  and  A1C13  appeared  to 
pass  through  the  membrane  at  a  relatively  greater  rate  than  the 
other  salts. 

3.  Comparisons  of  the  rate  of  passage  of  potassium  salts 
through  the  least  porous   membranes  (i.  e.,  with  pore  diam- 
eters of  about  0.7  microns)  in  the  case  of  dilute  solutions  gave  the 

//  /// 

following  anion  order  SO4  >C1  >FeC6N6.  For  concentrated 
solutions  the  order  for  the  least  porous  membrane  was  Cl  > 

•/// 

SO4>FeC6N6.     This  latter  order  was  the  inverse  of  the  order 


45 

of  magnitude  of  maximum  osmose.  Comparison  of  the  rates 
of  passage  of  chlorides  into  the  water  compartment  showed  the 
cation  order  in  dilute  solution  to  be  Al  >  Ca  >  K.  Exactly  the 
opposite  order  K  >  Ca  >  Al  was  found  for  concentrated  solutions. 
The  order  for  magnitude  of  osmose  with  dilute  solutions,  bore 
no  apparent  relation  to  the  cation  diffusion  order,  however, 
the  order  of  magnitude  of  osmose  with  concentrated  solutions 
was  the  inverse  of  the  cation  diffusion  order. 

4.  With  medium  porous  membranes  (i.  e.,  with  pore  diam- 
eters of  about  0.93  microns)  the  anion  order  for  rate  of  diffu- 

sion of  potassium  salts  from  dilute  solutions  was  SC>4  >  Cl  > 
/// 

FeC6N6    and    with    concentrated    solutions   was    Cl  >  SO4  > 


e.  This  was  again  the  inverse  of  the  order  of  maximum 
osmose  for  concentrated  solutions.  The  cation  order  for  rate 
of  diffusion  was  Ca  >  K  >  Al  in  dilute  solutions,  and  Ca  >  Al  >  K 
in  concentrated  solutions. 

5.  For  very  permeable  membranes  (i.  e.,  with  pore  diameters 
of  about  1.6  microns),  comparison  of  the  amounts  of  potas- 

sium salts  diffused  during  the  period  of  maximum  osmose, 

/// 

showed  the  anion  order  to  be  Cl  >  SO4  >  FeC6N6  for  both 
dilute  and  concentrated  solutions.  This  order  is  the  inverse 
of  the  order  of  maximum  osmose.  For  chlorides,  the  cation 
order  with  the  most  porous  membrane  was  K  >  Ca  >  Al  in 
both  dilute  and  concentrated  solutions.  This  order  was  the 
same  as  the  maximum  osmose  order  in  very  dilute  solutions, 
but  was  the  converse  of  the  order  of  maximum  osmose  in  con- 
centrated solutions. 

6.  If  the  pore  diameter  of  an  unstretched  membrane, 
i.  e.,  one  not  subjected  to  the  high  pressures  such  as  were  used 
in  measuring  pore  diameters,  is  as  we  believe,  slightly  less  than 
the   diameter   as   measured   with   the   stretched   membrane, 
these  membranes  then  have  pore  diameters  of  just  about  the 
same   magnitudes  as  the  copper  ferrocyanide  membranes  in- 
vestigated by  Bar  tell67  which  were  on  the  border  line  between 
osmotic  effect  and  no  osmotic  effect. 

67  Bartell:  Jour.  Phys.  Chem.,  16,  318  (1912). 


46 

7.  Tinker18  made  a  microscopic  study  of  copper  ferro- 
cyanide  gels  and  found:    "The  structure  seems  to  be  that  of  a 
somewhat  irregular  network  having  a  mesh  of  the  order  0.5 
to  1.0  microns.     In  this  respect,  it  seems  to  be  similar  to  most 
of  the  other  ordinary  gels,  such  as  gelatine,  silicic  acid,  etc., 
which  have  been  examined  with  great  thoroughness  by  Butschli, 
Hardy,  van  Bemmelen,  von  Weimarn,  Quincke,  Zsigmbndy, 
Pauli  and  others.     There  seems  to  be  a  general  agreement  at 
the  present  time  that  most  gels  consist  of  a  lattice  work  sys- 
tem in  which  a  solid  or  semi-solid  phase  encloses  a  more  liquid 
phase."     The  results  of  this  investigation  tend  to  corroborate 
the  above  view.     The  lattice  work  of  the  collodion  membrane 
may  be  formed  in  such  a  manner  that  the  net  work  forms  a 
mesh  of  the  order  0.5  to  1.0  microns.     If  the  liquid  phase  is 
replaced  by  water  when  the  lattice  work  is  of  this  order  the 
lattice  work  remains  unaltered  for  months  even  though  con- 
stantly subjected  to  nitration  tests. 

8.  The  work  described  in  this  section  has  clearly  brought 
out  the  fact  that  the  pore  diameter  of  an  osmotic  membrane 
is  a  highly  important  factor  in  determining  the  exact  nature 
of    osmose.     Furthermore,   it  seems  probable  that  the  phe- 
nomena of  anomalous  osmose  and  the  attending  salt  diffusion 
is  governed  largely  by  the  precise  pore  diameter  of  the  osmotic 
membrane. 


V.     EFFECT  OF  STIRRING  SOLUTIONS  DURING 
OSMOSIS 

The  experimental  work  described  in  this  section  of  the  thesis 
was  undertaken  to  test  further  the  hypothesis  of  the  author  that 
passage  of  solute  through  the  membrane  was  largely  respon- 
sible for  the  N  shaped  curves  observed  with  collodion  mem- 
branes. If  this  hypothesis  is  correct,  we  shall  expect  that  even 
with  the  least  permeable  collodion  membrane  (pore  diameter 
=  0.7  micron)  the  N  shaped  curve  will  be  initially  apparent  in 
the  case  of  potassium  salts  when  the  solutions  are  stirred.  In 


47 

addition,  we  should  expect  a  much  greater  positive  osmose  in 
the  shaken  cell  with  potassium  salts  giving  the  correct  elec- 
trical orientation  for  abnormally  positive  osmose,  for  the  rea- 
son that  in  the  shaken  cell,  diffused  solute  should  be  rapidly 
removed  from  the  face  of  the  membrane  on  the  water  side, 
thereby  maintaining  a  greater  potential  and  concentration 
gradient  across  the  membrane.  In  the  cases  of  CaCl2  and 
Aids,  salts  giving  an  electrical  orientation  favorable  to  neg- 
ative osmose,  we  shall  expect  a  greater  negative  effect  in  the 
shaken  than  in  the  stationary  cell.  Diffusion  of  solute  in 
the  shaken  cell  may  be  so  augmented  by  the  effect  of  the  con- 
tinuous stirring  that  an  N  shaped  osmose  curve  may  also  be 
observable  with  A1C13,  which  hitherto  has  shown  no  such 
tendency  in  our  experiments  with  membranes  of  different  pore 
size. 

It  has  been  shown  by  Kahlenberg21  that  the  osmose  rate 
is  materially  changed  by  stirring  the  solution  in  the  cell. 
Cohen  and  Commelin68  also  report  osmose  experiments  in  which 
the  solutions  were  stirred,  but  they  could  not  duplicate  their 
results.  A  decided  change  in  osmose  values  has  often  been 
observed  in  this  laboratory  when  the  stationary  osmose  cells 
have  been  accidentally  disturbed. 

The  contents  of  the  osmose  cell  of  the  T-type  was  found 
to  be  stirred  to  uniform  composition  very  quickly  by  placing 
a  metal  ball  in  each  compartment,  then  rocking  the  entire 
cell  slowly  back  and  forth.  This  method  of  stirring  possessed 
none  of  the  mechanical  difficulties  such  as  are  encountered  when 
externally  driven  rotary  stirrers  are  used.  Changes  in  con- 
centration in  each  compartment  of  the  cell  were  noted  by 
measuring  the  conductivity  of  the  solutions. 

Construction  and  Assembly  of  Rocking-  Cell 

The  construction  of  the  cell,  shown  in  Figure  13,  was  the 
same  as  used  in  our  previous  work  with  the  exception  of  the 
introduction  of  two  circular  platinum  electrodes,  connections 

68  Cohen  and  Commelin:  Zeit.  phys.  Chem.,  64,  1  (1908). 


48 


to  which  were  made  through  glass  inseals  in  each  compartment. 
The  inseal  glass  tubing  was  cut  off  at  an  appropriate  length  so 
as  to  serve  as  a  mercury  cup  through  which  electrical  contact 
with  the  outside  of  the  cell  could  be  established. 

The  cell  was  assembled  in  the  usual  manner.  The  plati- 
nizing of  the  electrodes  and  the  washing  was  done  in  the  usual 
way  and  before  the  membrane  was  put  in  place.  The  as- 
sembled cell  was  rinsed  with  several  changes  of  water  and  then 
placed  under  an  hydrostatic  pressure  to  clean  the  membrane 
capillaries. 

The  conductivity  constant  for  each  chamber  of  the  cell 
was  determined  before  each  pair  of  osmotic  experiments 


Fig.  13 
Osmose  Cell,  Rocking-Type  with  Electrodes 

(M/50  KC1  solution  being  used  for  this  purpose).  It  was 
found  that  the  specific  conductance  of  the  M/50  KC1  at  first 
changed  gradually  at  constant  temperature.  This  was  traced 
to  adsorption  of  KC1  from  the  solution  by  the  membrane.  It 
was  found  necessary  to  allow  the  membrane  to  come  to  equi- 
librium with  the  KC1  solution  after  which  this  solution  was 
replaced  with  fresh  KC1  solution  before  the  cell  constant 
could  be  determined.  This  manipulation  was  found  to  yield 
reproduceable  results.  After  the  cell  constant  had  been  de- 
termined, the  cell  was  rinsed  with  water  several  times,  and  then 
the  hydrostatic  pressure  applied;  finally  the  cell  was  again 
rinsed  with  conductivity  water. 


49 

The  Thermostat  and  Rocking  Machine 

The  thermostat  was  a  large  air  bath,  approximately  2  x  4  x 
6  feet  high,  electrically  heated,  and  cooled  by  a  large  metal 
cold  water  coil.  Rapid  circulation  of  air  was  maintained  by 
an  electric  fan.  The  temperature  was  250=t0.02°  C.  During 
operation  the  current  in  the  heater  was  thrown  off  and  on  by  a 
sensitive  toluene  regulator  approximately  every  five  seconds. 
Within  the  thermostat  was  an  electric  motor  which  through 
reducing  gears  drove  the  rocking  platform,  which  carried  the 
osmotic  cell,  at  a  slow  and  even  rate.  Uprights  were  attached 
to  the  platform,  and  carried  between  them  a  cross  piece  with 
narrow  slots  cut  at  the  proper  distance  to  support  the  osmo- 
meter  tubes.  Two  coiled  wire  springs  of  equal  tension  were  at- 
tached from  the  base  of  the  apparatus  to  each  side  of  the  up- 
right. This  avoided  any  jerking  motion  of  the  rocking 
platform  during  operation. 

The  front  and  one  side  of  the  thermostat  were  of  glass. 
The  front  was  in  two  sections,  the  upper  and  lower  halves  of 
which  could  be  raised  or  lowered  as  occasion  required. 

Method  of  Setting  up  Cell  for  Experiment 

Previous  to  setting  up  the  cell,  the  solutions  and  conduc- 
tivity water  to  be  used  were  allowed  to  come  to  the  tempera- 
ture of  the  thermostat.  The  long  osmometer  tubes  were  then 
half  filled  with  solution  or  water,  depending  on  the  chambers 
with  which  they  were  to  be  used.  Each  compartment  of 
the  osmose  cell  was  then  rinsed  twice  with  the  solution  it  was 
to  contain,  filled  with  solution,  air  bubbles  removed  and  a 
monel  metal  ball  lowered  into  each  compartment.  The  osmo- 
meter tubes  were  next  inserted  and  adjusted  to  the  same  level. 
The  apparatus  was  then  fastened  onto  the  rocking  platform 
and  the  stoppers  of  the  osmometer  tubes  waxed  into  place. 

At  the  close  of  an  experiment,  the  rocking  machine  was 
stopped,  the  cells  taken  out  and  the  solutions  and  metal  balls 
removed  by  taking  out  the  stoppers  in  the  two  ends  of  the 
cell.  The  osmometer  tubes  were  then  removed  and  the  cell 
washed  in  the  usual  manner. 


50 


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Osmose  Results  in  the  Rocking1  Cell 

Readings  were  taken  every  half  hour  for  the  first  two 
hours  and  then  every  two  hours  thereafter,  until  maximum 
osmose  values  were  reached.  The  results  at  the  end  of  the 
two  hour  period,  twelve  hour  period  and  maximum  osmose 
are  given  in  Tables  XI  and  XII.  Comparisons  of  the  effect  of 
stirring  and  not  stirring  on  the  osmose  of  A1C13  and  K3FeC6N6 
are  shown  in  Figures  14  and  15,  respectively. 

The  following  generalizations  concerning  the  effects  of 
stirring  on  osmose  were  disclosed  by  the  foregoing  data. 

1 .  The  shape  of  the '  'initial  osmose — concentration  curves' ' 
(2  hour  readings)  and  the  '  'maximum  osmose — concentration 
curves"  for  the  potassium  salts,  were  of  the  N  type  throughout 

and  were  more  strongly  ac- 
centuated than  when  the  solu- 
tions were  not  stirred. 

2.  With  dilute  solutions 
stirring   increased  both  the 
initial  and  maximum  osmotic 
effects  in   the    case   of   KC1, 
CaCl2,    and    K2SO4,   but    de- 
creased the  effect  with  AlCls 
and  the  maximum  effect  with 
K3FeC6N6. 

3.  With     concentrated 
solutions    of    electrolytes, 
greater  than  0.1    M,  stirring 
had    but    little    influence  on 
either  the  initial  rate  or  maxi- 
mum osmose. 

4.  Stirring  produced  a 
tendency  toward  the  N  shaped 
curve  even  in  the  case  of  AlCla 

Fig.  14  which  tendency  hitherto  had 

Osmose  Rate  of  A1CU  comparing  Effect    not  been  observed, 
of  Stirring  vs.  not  Stirring  Solutions  5.   With     SUCrose     SOlu- 


52 


tions,  stirring  increased  the  initial  osmose  rate,  but  decreased 
the  maximum  osmose. 

6.  The  above  results  are  in  harmony  with  the  hypothesis 
that  passage  of  solute  through  the  membrane  is  largely  re- 
sponsible for  the  appearance  of  the  N  shaped  curve  in  osmosis 
through  collodion  membranes. 

Passage  of  Salt  through  the  Membrane  during*  Osmose 
in  the  Rocking-  Cell 

For  the  purpose  of  measurement  of  the  concentration  of 
solute  in  each  compartment  during  the  osmotic  process,  the 

specific  conductance  of  the  re- 
spective solutions  was  deter- 
mined. The  specific  conduc- 
tance of  the  various  electro- 
lytes was  calculated  at  all 
known  dilutions  from  molar 
and  equivalent  conductivity 
data  already  published  by 
Kohlrausch69  and  Jones.70 

It  was  originally  planned 
to  determine  the  hydrogen 
ion  concentration  of  each  com- 
partment  as  osmose  de- 
veloped. It  was  believed  that 
this  might  throw  some  light 
on  the  problem.  This  would 
be  of  particular  interest  in 
cases  of  highly  hydrolyzable 
salts,  such  as  A1C13,  where  the 

Osmose  Rate  of  KsFe  (CN)6  comparing    HC1  Undoubtedly   passes  into 

Effect  of  stirring  vs.  not  Stirring        the  water  compartment  more 

rapidly  than  A1(OH)3.     These 

data  could  not  be  obtained  in  the  time  available  for  this  re- 
search, but  a  correction  can  be  applied  to  the  conductivity 


8//-Y //// 


~'      MOLAR  COHCENTRAT/ON 


69  Kohlrausch  and  Holborn:  "Leitvermogen  der  Elektrolyte"  (1898). 

70  Jones:   Carnegie  Institute  of  Washington,  Publ.  170  (1912). 


53 


measurements  hereinafter  given,  from  data  which  may  be  pre- 
sented at  some  future  time. 

The  ratio  of  salt  concentrations  on  the  two  sides  of  the 
membrane  was  calculated  from  conductivity  measurements 
for  the  two  hour  period  and  also  for  the  maximum  osmose 
period.  Several  experiments  continued  beyond  the  maximum 

TABLE  XIII 

Molar  Concentrations  of  Solutions  Two  Hours  after  starting  Osmose 

Experiment 
Rocking  Cell 


Salt 
solution 

Initial  molar 
cone,  of  salt 

Molar  cone,  of 
salt.    Compart- 
ment Ci 

Molar  cone,  of 
salt.     Compart- 
ment Ca 

Ratio 
Qi/Ci 

K3FeC6N6 

0.001 

0.000981 

0.0000212 

46.3 

0.004 

0.0*03795 

0.000218 

17.4 

0.01 

0.00919 

0.000862 

10.65 

0.1 

0.0907 

0.01036 

8.76 

0.5 

0.422 

0.0597 

7.29 

K2S04 

0.001 

0.000956 

0.0000405 

23.6 

0.004 

0.003806 

0.000248 

15.3 

0.01 

0.00907 

0.000947 

9.58 

0.1 

0.0879 

0.01201 

7.31 

0.5 

0.4151 

0.0760 

5.47 

KC1 

0.001 

0.000977 

0.0000768 

12.7 

0.004 

0.00347 

0.000613 

5.65 

0.01 

0.00872 

0.00152 

5.75 

0.1 

0.0784 

0.0183 

4.77 

0.5 

0.423 

0.1195 

3.54 

CaCl2 

0.001 

0.000971 

0.0000684 

14.0 

0.004 

0.00373 

0.000443 

8.42 

0.01 

0.00899 

0.00124 

7.25 

0.1 

0.0899 

0.0124 

7.25 

0.5 

0.456 

0.0661 

6.89 

A1C13 

0.002 

0.00178 

0.000198 

9.0 

0.008 

0.00674 

0.000671 

10.03 

0.02 

0.01601 

0.00165 

9.71 

0.2 

0.1628 

0.0219 

7.43 

osmose  period  showed  that  eventually  identical  concentra- 
tion in  both  chambers  was  reached  and  at  this  point 
the  osmose  value  had  diminished  to  zero.  The  "least  per- 
meable" membranes  were  used  throughout  this  part  of  the 
work. 


54 


Summary 

The  foregoing  data  warrant  the  following  conclusions: 

1.  Stirring  increased  the  rate  of  passage  of  all  electrolytes 

through  the  membrane  at  all  concentrations.     The  relative 

increase  in  diffusion  rate  due  to  stirring  was  greatest  in  dilute 

solutions. 

TABLE  XIV 

Molar  Concentrations  of  Solutions  when  Maximum  was  registered 

Rocking  Cell 


Salt 
solution 

Initial  molar 
cone,  of  salt 

Molar  cone,  of 
salt.     Compart- 
ment Ci 

Molar  cone,  of 
salt.     Compart- 
ment C2 

Ratio 

Q/C, 

K3FeC6N6 

0.001 

0.000761 

0.000183 

4.16 

0.004 

0.  '002378 

0.001384 

1.72 

0.01 

0.00595 

0.003876 

1.53 

0.1 

0.0635 

0.0438 

1.45 

0.5 

0.2973 

0.2128 

1.40 

K2SO4 

0.001 

0.00746 

0.000276 

2.70 

0.004 

0.002526 

0.001662 

1.52 

0.01 

0.005895 

0.00424 

1.39 

0.1 

0.0676 

0.03868 

1.75 

0.5 

0.2966 

0.2190 

1.35 

KC1 

0.001 

0.000640 

0.000471 

1.356 

0.004 

0.002315 

0.001755 

1.320 

0.01 

0.00612 

0.00410 

1.493 

0.1 

0.0546 

0.0426 

1.281 

0.5 

0.2765 

0.2338 

1.182 

CaCl2 

0.001 

0.000792 

0.000237 

3.34 

0.004 

0.003024 

0.001237 

2.45 

0.01  . 

0.00618 

0.00420 

1.47 

0.1 

0.0656 

0.0432 

1.52 

0.5 

0.3182 

0.2300 

1.38 

A1C13 

0.002 

0.00121 

0.000714 

1.70 

0.008 

0.00445 

0.003017 

1.47 

0.02 

0.0088 

0.00658 

1.65 

0.2 

0.1154 

0.0803 

1.44 

2.  The  rate  of  passage  of  solutes  into  the  water  compart- 
ment was  greater  for  concentrated  solutions  than  dilute,  but 
in  no  case  proportional  to  concentration,  except  in  two  cases 
with  CaCl2. 

3.  In  the  region  of   0.01    M   concentration,  the  percent 


55 


increase  in  mols  of  salt  passing  through  the  membrane  in  two 
hours,  due  to  stirring,  was  as  follows:  KC1  140,  K2SO4  13, 
K3FeC6N6  63,  CaCl2  72,  A1C13  95. 

4.  The  ratio  of  concentrations  of  solute  in  the  two  com- 
partments decreased  in  magnitude  as  osmose  progressed.     In 

TABLE  XV 

Millimols  of  Salt  passing  through  Least  Permeable  Membrane  into 
Water  Compartment  during  Two  Hour  Osmose  Period 


Salt 

Initial  molar 
cone,  in  salt 
compartment 

Stationary  cell 
A 

Rocking  cell 
B 

B 

A 

K3FeC6N6 
K2S04 
KC1 
CaCl2 
AlCla 

0.001 
0.004 
0.01 
0.1 
0.5 
0.001 
0.004 
0.01 
0.1 
0.5 
0.001 
0.004 
0.01 
0.1 
0.5 
0.001 
0.004 
0.01 
0.1 
0.5 
0.002 
0.008 
0.02 
0.2 

0.00036 
0.00371 
0.01465 
0.1760 
0.9840 
0.00069 
0.00421 
0.0163 
0.2040 
1.291 
0.00130 
0.0104 
0.0258 
0.3110 
2.032 
0.00118 
0.00755 
0.02105 
0.2105 
1.125 
0.00336 
0.01141 
0.02801 
0.3722 

0.0015 
0.0090 
0.164 

2.46 
1.62 
1.07 

0.0034 
0.0144 
0.1803 

1.23 
1.13 
1.15 

0.0020 
0.0107 
0.217 

5.20 
2.41 
1.33 

0.00275 
0.01225 
0.199     . 

2.76 
1.73 
1.05 

0.00587 
0.0234 
0.282 

1.94 
1.21 
1.32 

concentrated  solutions  this  ratio  approached  1 : 1  (approx- 
imately 1:  1.4)  at  the  maximum  osmose  period.  For  more 
dilute  solutions,  this  ratio  remained  much  greater. 

5.  With  potassium  salts,  the  relation  of  anion  valence  to 
rate  of  passage  of  electrolyte  through  the  membrane  showed 


56 

the  following  order  in  each  case:  Cr>SO4'r>FeG6N6'/.  This 
order  was  the  same  at  all  concentrations  and  was  the  inverse 
of  the  order  of  magnitude  of  maximum  osmose.  With  chlor- 
ides, the  cation  order  was  K>Ca>Al  at  all  concentrations. 
This  cation  order  was  the  inverse  of  the  order  of  magnitude  of 
maximum  osmose  in  concentrated  solutions.  The  above  orders 
were  the  same  as  those  obtained  when  the  solutions  were  not 
stirred. 

6.  Stirring  does  accentuate  the  N  shaped  osmose  curve. 


VI.     GENERAL  SUMMARY. 

1.  The  theory  of  anomalous  osmose   as   advanced  by 
Bartell  and  co-workers  has  been  examined  with  respect  to 
collodion  membranes  and  found  to  apply. 

2.  Certain  anomalous  effects  involving  time  as  a  factor 
in  their  appearance  (the  N  shaped  curves  in  the  advance  stage 
of  osmose),  not  directly  covered  by  the  above  theory,  have 
been  shown  to  be  due  to  the  passage  of  solute  through  the 
membrane   into    the   water   compartment.      This   materially 
alters   the  potential  and '  concentration  gradients  across  the 
membrane  and  gives  the  observed  abnormal  osmotic  effects. 


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UNIVERSITY  OF  CALIFORNIA  UBRARY 


